PC-NRLF 


3E   013 


A  TREATISE  OF  ELECTRO-CHEMISTRY. 

EDITED  by  BERTRAM  BLOUNT,  F.I.C.,  ETC. 


THE  MANUFACTURE  OF  CHEMICALS 
BY  ELECTROLYSIS 


A  TREATISE  OF  ELECTRO-CHEMISTRY. 

EDITED  by  BERTRAM  BLOUNT,  F.I.C.,  ETC. 


THE 

MANUFACTURE   OF   CHEMICALS 
BY   ELECTROLYSIS 


BY 


ARTHUR  J.  HALE,  B.Sc,  F.I.C. 

CHIEF  ASSISTANT   IN    THE  CHEMICAL  DEPARTMENT,  CITY  AND  GUILDS  TECHNICAL 
COLLEGE,   FINSBURV 


NEW  YORK 
D.     VAN     NOSTRAND     CO. 

TWENTY-FIVE  PARK  PLACE 
1919 


EDITOR'S  PREFACE. 

THE  idea  of  a  series  of  books  on  Electro-Chemistry 
emanated  not  from  me,  but  from  Messrs.  Constable. 
Some  years  back  I  wrote  for  them  a  book  called 
"  Practical  Electro-Chemistry,"  intended  to  cover 
a  great  part  of  the  ground  of  knowledge  then  ex- 
tant. Fortunately,  knowledge  has  a  habit  of  grow- 
ing and  of  propagating  its  kind,  and  my  book,  in 
consequence  of  this,  became  a  "  back  number  ". 

The  subject  of  Electro-Chemistry  is  so  ramified 
and  specialized  that  it  was  impossible  for  one  man 
to  make  a  survey  of  the  whole  field.  This  fact  is 
the  genesis  of  the  present  series  in  which  those 
who  have  accurate  and  intimate  knowledge  of  the 
various  branches  of  electro-chemistry  have  under- 
taken the  work  for  which  they  are  particularly 
qualified.  It  will  be  readily  understood  that,  as 
the  series  of  books  was  started  at  an  early  period 
of  the  war,  many  contributors  were  engaged  in 
work  of  national  and  primary  importance,  and 
were  unable,  however  willing,  to  apply  themselves 
at  the  moment  to  exacting  literary  work.  But  this 
difficulty  was  gradually  overcome,  as  some  pro- 
spect of  a  period  to  the  struggle  came  within  view, 

434857 


VI  PREFACE. 

with  the  result  which  the  reader  will  judge  with 
consideration  for  the  onerous  conditions  under 
which  my  contributors  have  wrought. 

The  monographs  resulting  from  their  labours 
speak  for  themselves,  and  if  the  educational  advan- 
tages which  I  have  obtained  from  reading  them 
during  their  passage  through  the  press  is  shared  by 
the  public,  I  believe  that  the  thorough  and  modern 
work  of  my  friends  and  collaborators  will  be  ap- 
preciated, and  such  faults  as  there  be  will  be 
attributed  to  the  person  ultimately  responsible 
— the  Editor. 


PREFACE. 

THE  manufacture  of  chemicals  by  electrolysis  is 
now  sufficiently  important  to  justify  the  appear- 
ance of  a  monograph  dealing  with  the  subject. 
The  author  has  given  a  complete  and  up-to-date 
account  of  processes  now  in  use,  and  it  is  hoped 
that  the  matter  has  been  so  presented  as  to  indi- 
cate, to  some  extent,  future  developments. 

There  are  many  signs  that  industrial  chemists 
realise  the  importance  of  electrolysis  in  the  manu- 
facture of  organic  chemicals,  and  the  author  has 
endeavoured  to  portray  clearly  the  present  posi- 
tion of  this  branch  of  the  subject. 


A.  J.  H. 


LONDON, 

January,  1919. 


CONTENTS. 

CHAPTER  I. 

ELECTROLYTIC  HYDROGEN  AND  OXYGEN.     OZONE. 

PAGE 

General  principles.  PLANT  AND  APPARATUS  FOB  THE  ELECTROLYSIS  OP 
WATER  :  Apparatus  of  D'Arsonval — Apparatus  of  Latchinoff — 
Apparatus  of  Renard.  MODERN  PLANT:  Schmidt  process — 
Schoop's  plant — Process  of  Garuti — Schuckert  process — Hazard- 
Flamand  process — Cell  of  International  Oxygen  Company. 
Modern  filter-press  cells.  Electrolytic  production  of  ozone  .  1 

CHAPTER  II. 

PRODUCTION  OF  PER-SALTS  AND  HYDROGEN 
PEROXIDE. 

Persulphates  and  persulphuric  acid.  Hydrogen  peroxide.  Percar- 
bonates.  Perborates.  Potassium  permanganate.  Potassium 
ferricyanide.  Electrolytic  sulphuric  acid.  Sodium  selenate  .  17 

CHAPTER  III. 

NITRIC  ACID.    HYDROXYLAMINE.     HYDROSULPHITES. 
FLUORINE. 

Nodon's  process  for  nitric  acid.  REDUCTION  OP  NITRIC  ACID:  Hy- 
droxylamine  —  Nitrites.  Sodium  hydrosulphite.  Electrolytic 
production  of  fluorine 30 


CHAPTER  IV. 

ELECTROLYTIC  PREPARATION  OF  PIGMENTS  AND 
INSOLUBLE  SUBSTANCES. 

PRECIPITATION  OP  METALLIC  OXIDES  :  Work  of  Lorenz — Luckow's 
improvement — Lead  chromato — Lead  sulphate  —Lead  peroxide- 
White  lead — Zinc  white.  Separation  of  rare  earth  oxides.  Pyro- 
phoric  alloys.  Tungsten  bronzes 40 

ix  b 


X  CONTENTS. 

CHAPTER  V. 

ELECTRO-OSMOTIC  AND  ELECTRO-COLLOIDAL 
PROCESSES. 

PAGE 

General.  Dehydration.  Separation  of  constituents  of  glue.  Tan- 
ning of  skins.  Purification  of  silicic  acid.  Alumina.  Electro- 
lytic lixiviation.  Principles  of  electro-osmosis  .  .  .  .49 

CHAPTER  VI. 

ELECTROLYTIC  REDUCTION  OF  ORGANIC  COMPOUNDS. 

Introductory.  REDUCTION  OP  NITRO-COMPOUNDS  :  Aminophenols — 
Chloranilines — Amines — Benzidine — Azoxybenzene — Azobenzene 
— Hydrazobenzene — Importance  of  electrode  potential — Catalytic 
action  of  cathode — Overvoltage — Reduction  in  aqueous-alkaline 
emulsions — Production  of  aminophenols.  Hydrazines.  REDUC- 
TION OF  THE  CARBONYL  GROUP  :  Secondary  alcohols — Pinacones — 
Deoxycaffeine.  Hydrogenation  of  quinolines.  Indigo  white. 
jj-Rosaniline 53 

CHAPTER  VII. 

OXIDATION  AND  SUBSTITUTION  OF  ORGANIC 
COMPOUNDS. 

OXIDATION  PRODUCTS  :  Oxidation  of  aromatic  side  chains — Quinone — 
Basic  dyes — Purpurogallin — Anthraquinone — Vanillin — Saccha- 
rin. Oxidation  of  alcohols.  ELECTROLYTIC  SUBSTITUTION: 
lodofonn  —  Bromoform  —  Chloroform  —  Chloral  —  Diazo-com- 
pounds  —  Azo-dyes  —  Substituted  phenols.  CONDENSATION  BY 
ELECTROLYSIS  :  Esters  of  dicarboxylic  acids.  Effect  of  super- 
imposing alternating  current  on  direct  current  .  .  .  .65 

APPENDIX 75 

NAME  INDEX 77 

SUBJECT  INDEX  79 


ABBREVIATIONS  EMPLOYED  IN  THE 
REFERENCES. 


Amer.  Chem.  J.  . 

Annalen      . 

Ber 

Bull,  de  1'Assoc.  Ing.  Elect. 

Chern.  Zeit. 
Compt.  rend. 

D.B.P 

Electrochem.  Ind. 
Electrochem.  Review  . 
Electrochem.  Zeitsch. 

Eng.  Pat 

Fr.  Pat 

Int.  Cong.  App.  Chem. 

J.  Amer.  Chem.  Soc.  . 

J.  Physical  Chem. 

J.  pr.  Chem. 

J.  Soc.  Chem.  Ind.      . 

Met.  Chem.  Eng. 

Monatsh 

Rec.  trav.  chim. . 

Trans.  Amer.  Electrochem. 

Trans.  Chem.  Soc. 
Trans.  Farad.  Soc.      . 

U.S.Pat 

Zeitsch.  angew.  Chem. 
Zeitsch.  anorg.  Chem. 
Zeitsch.  Elektrochem. 
Zeitsch.  physikal  Chem.  . 


American  Chemical  Journal. 

Justus  Liebig's  Annalen  der  Chernie. 

Berichte  der  Deutschen  chemischen  Gesell- 
sohaft. 

Bulletins  de  1'Association  des  Ingenieurs 
Electriques. 

Cherhiker  Zeituug. 

Comptes  rendus  hebdomadaires  des  Stances 
de  1' Academic  des  Sciences. 

Deutsches  Reich  spatent. 

Electrochemical  Industry. 

Electrochemical  Review. 

Elektrochemische  Zeitschrift. 

English  Patent. 

French  Patent. 

International  Congress  of  Applied  Chemistry. 

Journal  of  the  American  Chemical  Society. 

Journal  of  Physical  Chemistry. 

Journal  fiir  praktische  Chemie. 

Journal  of  the  Society  of  Chemical  Industry. 

Metallurgical  and  Chemical  Engineering. 

Monatshefte  fiir  Chemie  und  verwandte 
Theile  anderer  Wissenschaften. 

Recueil  des  travaux  chimiques  des  Pays-Bas 
et  de  la  Belgique. 

Transactions  of  the  American  Electro- 
Chemical  Society. 

Transactions  of  the  Chemical  Society. 

Transactions  of  the  Faraday  Society, 

United  States  Patent. 

Zeitschrift  f  iir 'angewandte  Chemie. 

Zeitschrift  fiir  anorganische  Chemie. 

Zeitschrift  fiir  Elektrochemie. 

Zeitschrift  fiir  physikalische  Chemie. 


xi 


CHAPTEE  I 

ELECTROLYTIC  HYDROGEN  AND  OXYGEN.    OZONE. 

THE  electrolytic  decomposition  of  water  provides  a  suit- 
able introduction  to  the  manufacture  of  chemicals  by 
electrolysis.  Many  of  the  processes  described  herein  de- 
pend upon  the  employment  of  electrolytic  hydrogen  and 
oxygen,  and  the  electrolysis  of  water  furnishes  a  convenient 
subject  with  which  to  introduce  certain  fundamental  prin- 
ciples and  electrical  quantities. 

Since  1895  several  forms  of  apparatus  and  plant  have 
been  on  the  market  for  providing  hydrogen  and  oxygen  by 
electrolysing  water.  They  are  largely  employed  in  ac- 
cumulator works  where  the  oxy-hydrogen  flame  is  needed 
for  lead-welding,  and  also  in  metallurgical  processes  where 
a  high  temperature  flame  is  necessary  for  melting  refrac- 
tory metals  such  as  platinum. 

The  production  of  these  ,two  gases  by  electrolysis  for 
storage  and  transport  can  only  be  commercially  successful 
when  the  cheapest  power  is  utilised,  because  there  are 
established  economical  processes  for  making  both  oxygen 
and  hydrogen. 

Pure  water  is  practically  a  non-electrolyte,  and  in  order 
that  it  may  become  a  conductor,  a  small  quantity  of  acid, 

alkali,  or  soluble  salt  must  be  dissolved  in  it.     On  passing 

(1)  1 


a         THE   MANUFACTUEE   OF   CHEMICALS  BY  ELECTEOLYSIS 

a  continuous  current  of  electricity  at  a  pressure  of  about 
2  volts  between  metal  electrodes  immersed  in  the  solution, 
a  definite  volume  of  hydrogen  is  liberated  at  one  electrode, 
and  half  the  volume  of  oxygen  at  the  opposite  electrode. 
That  electrode  at  which  the  hydrogen  is  discharged  is 
known  as  the  cathode,  and  is  connected  with  the  negative 
pole  of  the  battery  or  machine  supplying  the  current.  The 
electrode  at  which  oxygen  is  discharged  is  the  anode,  and 
is  connected  with  the  positive  pole  of  the  current  source. 
The  decomposition  voltage  necessary  for  decomposing 
water  by  electrolysis  can  be  calculated  from  the  heat  of 
formation  which  is  68,400  calories.  Since  1  joule  or  1 
volt-coulomb1  is  equivalent  to  0'239  calorie,  the  electrical 
energy  necessary  for  decomposing  1  gram-molecule  of 

68400 
water  will  be    •*„*    =  285,714  volt-coulombs.      Two  equi- 

valents of  hydrogen  will  be  discharged,  and  this  amount 
will  require,  according  to  Faraday's  Law,  2  x  96500 
coulombs  of  electricity  ;  the  voltage  necessary  for  decom- 

position will  therefore  be  Tr^gggoJT  =  1  '48  volts.      Owing 


to  various  conductivity  losses  the  voltage  needed  between 
the  electrodes  in  the  various  forms  of  plant  varies  from 
1  -9  to  as  much  as  4  volts. 

The  solutions  generally  employed  are  dilute  sulphuric 
acid  (10-20  per  cent.)  or  dilute  alkali  solution  containing 
potassium  or  sodium  hydroxide,  and  sometimes  potassium 
carbonate  is  utilised  (10-25  per  cent). 

1  See  Appendix. 


ELECTKOLYTIC  HYDROGEN   AND   OXYGEN.      OZONE         3 

Experimentally  determined  minimum  voltages  necessary 
for  decomposing,  continuously,  such  aqueous  solutions  be- 
tween platinum  electrodes  approximate  closely  to  1*67  volts. 

Since  1  gram  of  hydrogen  is  liberated  by  the  passage 
of  96,500  coulombs  of  electricity,  therefore  1  amp. -hour 
(3600  coulombs)  will  liberate  0'037  gram  or  0'0147  cubic 
foot  at  normal  temperature  and  normal  atmospheric  pres- 
sure (N.T.P.).1 

The  amount  of  current  generally  passed  through  an  in- 
dustrial unit  is  about  400  amps.,  and  this  will  discharge 
approximately  400  x  '0147  =  5*88  cubic  feet  of  hydrogen 
per  hour  and  simultaneously  2 '94  cubic  feet  of  oxygen. 
This  amount  of  gas  will  be  discharged  by  400  x  T67  =  668 
watt-hours  or  0'668  K.W.H.,  hence  one  K.W.H.  will  dis- 
charge 8 '8  cubic  feet  of  hydrogen.  In  practice  the  volume 
of  hydrogen  obtained  is  4*5  -  8'25  cubic  feet  per  K.W.H. 

The  following  statement  will  convey  some  indication  of 
the  energy  utilised  annually  in  a  typical  installation 
designed  to  give  about  15,000  cubic  feet  of  hydrogen  per 
day :  If  the  working  day  be  24  hours  for  300  days  per 
annum,  the  yearly  output  will  be  15,000  x  300  =  4,500,000 
cubic  feet.  Each  cell  takes  about  400  amps,  at  2  volts, 
that  is,  0'8  K.W.H.  per  hour,  and  if  there  be  100  units 
in  the  plant,  the  energy  utilised  each  year  will  be 
100  x  -8  x  24  x  300,  or  576,000  K.W.H.  To  this  must 
be  added  approximately  25  per  cent,  to  allow  for  loss 

aThat  is  a  temperature  of  0°  CM  and  the  pressure  of  a  column  of  mer- 
cury 760  mm.  high  at  latitude  45°  and  at  sea  level ;  the  temperature  of  the 
mercury  being  0°  C. 


4        THE   MANUFACTUKE   OF   CHEMICALS   BY  ELECTROLYSIS 

through  the  motor  generator  employed,  making  a  total  of 
720,000  K.W.H.  per  year.  If  the  gases  are  to  be  com- 
pressed, 300  Ib.  per  sq.  inch  for  hydrogen  will  necessitate 
about  1-5  KW.H.  per  hour,  that  is,  1-5x24  x  300  =  10,800 
K.W.H.  per  year.  The  oxygen  is  usually  compressed  to 
1800  Ib.  per  sq.  inch,  and  this  will  require  4.5  K.W.H  per 
hour,  that  is,  4'5  x  24  x  300  =  32,400  K.W.H.  per  year. 
The  total  energy  required  will  be  720,000  +  10,800 
+  32,400  =  763,200  K.W.H.  per  year  in  the  production  of 
4,500,000  cubic  feet  of  hydrogen  and  2,250,000  cubic  feet 
of  oxygen.  At  the  rate  of  0'5d.  per  B.O.T.  unit  the  cost 
of  energy  per  annum  will  be  about  £1600. 

The  first  plant  devised  for  supplying  oxygen  was  that  of 
D'Arsonval,  of  the  Royal  College  of  France  (1885),  who 
employed  a  30  per  cent,  solution  of  potash  as  electrolyte. 

A  perforated  iron  cylinder  enclosed  in  a  sack  of  wool  or 
cotton  served  as  anode,  whilst  a  similar  iron  cylinder  was 
made  the  cathode.  The  apparatus  gave  about  150  litres 
of  oxygen  per  day. 

~  Latchinoff,1  of  Petrograd  (1888),  devised  the  first  ap- 
paratus for  collecting  both  gases  under  pressure,  and  he 
was  also  the  first  to  utilise  bipolar  electrodes.  In  his 
earlier  forms  of  apparatus,  he  employed  an  alkaline 
electrolyte  and  iron  electrodes,  or  15  per  cent,  sulphuric 
acid  with  carbon  cathodes  and  lead  anodes,  but  in  im- 
proved large-scale  plant  he  used  only  alkaline  solutions 
in  an  iron  tank  which  contained  a  number  of  bi-polar 
1  Elektrochem.  Zeitsch.,  1894, 1,  108  ;  D.B.P.  51998  (1888). 


ELECTROLYTIC  HYDROGEN  AND   OXYGEN.      OZONE          5 

iron  electrodes  separated  from  each  other  by  parchment 
sheets. 

Colonel  Eenard  of  Paris l  (1890)  prepared  hydrogen,  for 
balloon  work,  in  a  cylindrical  iron  cathode  vessel  in  which 
was  suspended  a  cylindrical  iron  anode  surrounded  by 
an  asbestos  diaphragm.  The  electrolyte  was  caustic  soda, 
and  250  litres  of  hydrogen  were  obtained  per  hour. 

The  first  modern  plant  was  introduced  by  Dr.  0.  Schmidt 2 
in  1899.  It  is  constructed  on  the  filter-press  principle,  and 


Fia.  1. 

is  manufactured  by  the  Machinenfabrik,  Oerlikon,  Zurich. 
Bi-polar  iron  electrodes  e  are  fixed  in  a  strong  iron  frame 
(Fig.  1)  and  are  separated  from  each  other  by  diaphragms 
of  asbestos  d,  which  are  bound  with  rubber  borders.  The 
electrodes  are  bordered  by  thick  rims,  so  that  when  close 
together  there  is  a  cavity  between  two  adjacent  plates 
which  is  divided  into  two  equal  portions  by  the  diaphragm, 
the  rubber  edge  of  which  serves  to  insulate  the  adjacent 

1  La  Lumtire  Electrique,  39,  39. 

2D.R.P.  111131  (1899);  Zeitsch.  Elektrochem.,  1900,  7,  296. 


6        THE   MANUFACTUEE   OF   CHEMICALS  BY  ELECTROLYSIS 

plates  from  each  other.  Two  holes  ho  (Fig.  2)  in  the  rim 
of  each  electrode  communicate  so  as  to  form  two  channels 
when  the  unit  is  made  up,  and  these  serve  to  convey  the 
hydrogen  and  oxygen  from  the  cells,  whilst  the  lower 
channels  WW,  formed  in  a  similar  manner,  serve  to 
supply  the  chambers  with  electrolyte. 

The  channels  h  and  W  communicate  with  the  cathode 
spaces  only,  whilst  o  and  W  connect  anode  spaces.     The 


o 


W 


w' 


FIG.  2. 


channels  WW  for  supplying  water  are  connected  with  a 
main  pipe  A,  and  at  the  other  end  of  the  unit  the  gas 
channels  ho  communicate  with  the  washing  chambers  H 
and  0.  The  stopcock  a,  shown  in  the  diagram  of  a  com- 
plete Schmidt  apparatus  (Fig.  3),  is  for  emptying  the  ap- 
paratus. The  electrolyte  recommended  is  a  10  per  cent. 
potassium  carbonate  solution,  and  is  probably  preferred  to 
the  corresponding  sodium  salt  on  account  of  its  freedom 
from  chloride,  which  exerts  a  corrosive  action  upon  the 
iron-work  of  the  apparatus. 


ELECTROLYTIC   HYDROGEN   AND   OXYGEN.      OZONE         7 

A  voltage  of  2*5  volts  is  maintained  between  adjacent 
electrodes,  and  the  energy  efficiency  is  stated  to  be  ap- 
proximately 54  per  cent.  The  hydrogen  generated  has  a 
purity  of  99  per  cent,  and  the  oxygen  purity  is  97  per  cent., 
but  this  can  be  raised  to  over  99  per  cent,  by  passing  the 
gas  over  platinum  at  100°  C. 

Standard  types  of  plant  are  manufactured  for  working 


FIG,  3. 

at  a  pressure  of  65  or  110  volts.  The  quantity  of  water 
decomposed  per  K.W.H.  is  about  130  c.c.,  and  this  loss 
must  be  made  good  continuously  to  prevent  the  electrolytic 
gases  from  collecting  in  the  cells.  A  Schmidt  plant  for 
generating  33  cubic  metres  of  oxygen  per  twenty-four 
hours  costs  about  £6000,  and  for  immediate  use  without 
compression  the  cost  of  the  electrolytic  gas  per  cubic  metre 
(35  cubic  feet)  is  approximately  5d.  to  6d. 
The  conductivity  of  an  alkaline  electrolyte  is  lower  thai) 


8        THE   MANUFACTUEE   OF   CHEMICALS  BY  ELECTEOLYSIS 

that  of  20-30  per  cent,  sulphuric  acid,  but  it  has  the  great 
advantage  that  it  is  without  corrosive  action  on  iron,  and 
therefore  plant  can  be  constructed  of  iron  or  steel  with 
electrodes  of  the  same  material  when  an  alkaline  liquid  is 
employed. 

Moreover,  when  lead  is  used  for  the  electrodes,  as  it  must 
be  with  a  sulphuric  acid  electrolyte,  considerable  over- 
voltage  occurs  at  the  electrodes ;  hence,  in  spite  of  increased 
conductivity  the  economy  in  energy  is  negligibly  small. 

Great  difficulty  has  been  experienced  by  all  inventors  in 
constructing  a  cell  which  will  effectually  prevent  any 
mixing  of  the  gases  evolved  and  the  formation  of  a  danger- 
ously explosive  mixture.  This  point,  it  will  be  observed, 
receives  special  attention  in  all  the  cells  described. 

SCHOOP'S  PLANT.1 

In  this  cell  dilute  sulphuric  acid  is  employed,  and  the 
electrodes,  as  well  as  the  containing  vessel,  are  constructed 
of  lead.  Each  electrode  is  encased  in  an  earthenware  tube 
which  is  perforated  round  its  lower  portion,  and  sealed  at 
the  top  with  insulating  material.  Each  electrode  is  thus 
completely  separated  from  the  rest,  and  intermixture  of 
the  gases  is  rendered  impossible.  Dilute  sulphuric  acid 
(density  1 '235)  is  the  electrolyte  employed,  and  the  voltage 
required  for  each  unit  is  about  3 '9  volts.  The  diagram 
(Fig.  4),  which  shows  a  section  through  two  cells,  will 
explain  the  construction. 

Each  unit  consists  of  a  lead-lined  vat  which  contains 

1  J.  Soc.  Chem.  Ind.,  1901,  20,  258  ;  D.B.P.  141049  (1901) ;  Electrochem. 
Ind.,  1902, 1,  297. 


ELECTEOLYTIC   HYDEOGEN   AND   OXYGEN.      OZONE 


two  cylindrical  lead  anodes  and  two  corresponding  cathodes. 
Each  electrode  contains  a  bundle  of  lead  wires  which  give 
increased  electrode  surface,  and  the  lower  part  of  the 
electrode  is  perforated  to  give  free  access  to  the  current 
and  to  the  electrolyte.  For  the  same  reason  each  surround- 
ing earthenware  tube  is  perforated  round  its  lower  portion. 


d 

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r 

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7  r 

7 

00 

, 

s 

i 

0°° 

i 

0* 

I 

!o 

i 

?o 

i 
i 

OQ 
^0 

0° 

1 

Jj 

i 

j 

<PO 

j 

Of 

DO 
00 

• 

— 

PO 

£o 

• 

— 

B 

00 

.2 

^1     > 

^ 

: 

&< 

f 

j 

FIG.  4. 

The  apparatus  can  be  constructed  with  iron  electrodes 
for  use  with  an  alkaline  electrolyte,  and  the  working 
voltage  is  then  about  2'25  volts  as  compared  with  3*8  volts 
for  sulphuric  acid  and  electrodes  of  lead. 

The  following  costs  are  quoted  by  the  makers  for  plant 
with  acid  electrolyte:  One  H.P.  hour  gives  97'5  litres  of 
hydrogen  and  half  this  amount  of  oxygen ;  or,  stated  in 
another  way,  1  cubic  metre  of  the  mixed  gases  requires 


10      THE   MANUFACTUEE   OF  CHEMICALS  BY  ELECTEOLYSIS 

6'2  to  6'8  H.P.  hours  of  energy  costing  3-3'5d.  With  an 
alkaline  electrolyte  and  iron  electrodes  the  cost  is  even 
lower.  The  generated  oxygen  has  a  purity  of  99  per  cent, 
and  the  hydrogen  97 '5-98  per  cent. 

PEOCESS  OF  GAEUTI. 

The  plant  invented  by  Garuti  and  Pompili  in  1893  is  a 
well-known  type  in  which  iron  electrodes  are  employed 
with  alkaline  electrolyte. 

Anodes  and  cathodes  are  connected  in  parallel,  and  the 
diaphragms  separating  the  electrodes  from  each  other  are 
iron  sheets  perforated  near  the  lower  edge.  The  successful 
working  of  this  arrangement  depends  on  the  fact,  first 
ascertained  by  Del  Proposto,1  that  if  the  voltage  between 
the  electrodes  is  not  above  3  volts,  the  iron  diaphragm 
between  them  does  not  become  bipolar,  and  hence  no  gas 
is  evolved  on  its  surface. 

In  the  cells  constructed  by  Garuti 2  and  Pompili  prior 
to  1899  lead  electrodes  were  employed,  and  the  electrolyte 
was  sulphuric  acid  solution  which  was  contained  in  a  lead- 
lined  wooden  tank,  but  this  was  abandoned  ultimately  for 
iron  construction  and  an  alkaline  electrolyte. 

The  outer  case  and  electrode  system  are  made  of  iron. 
In  Fig.  5  a  longitudinal  vertical  section  is  shown,  in  which 
B  represents  the  iron  casing  holding  the  electrodes  and 
diaphragms.  The  spaces  H  and  0  are  bells  in  which  the 
hydrogen  and  oxygen  respectively  collect  before  rising 

1  Bull,  de  VAssoc.  des  Ingen.  Electr.,  1900,  11,  805. 

2  L'Industrie  Electrochimique,  1899, 11,  113 ;  Eng.  Pats.  16588  (1892), 
23663  (1896),  12950  (1900),  2820  (1902),  27249  (1903). 


ELECTROLYTIC   HYDROGEN   AND  OXYGEN.      OZONE       11 

through  the  exit  tubes  TT'.  The  electrodes  and  diaphragms 
traverse  the  entire  length  of  B  and  are  shown  sectionally 
in  Fig.  6,  which  is  a  transverse  section.  Electrodes  e  are 


Y////A 


FIG.  5. 


12  mm.  apart,  and  the  lower  edge  of  each  is  12  cms.  from 
the  bottom  of  the  tank.  Each  diaphragm  d  has  a  zone  of 
perforations  4  cms.  wide  running  parallel  with  and  about 


H 
d  d 

'•s/'  •v—v'  "N/^NX  \/— ^  N 


FIG.  6, 


7 '5  cms.  above  the  lower  edge.  Anode  spaces  open  at  the 
top,  on  one  side,  into  the  bell  0  which  receives  oxygen,  and 
in  a  similar  manner  the  cathode  spaces  open  on  the  other 
side  to  the  bell  H  which  collects  hydrogen  (see  Fig.  5). 


12      THE   MANUFACTUEE   OF   CHEMICALS   BY  ELECTBOLYSIS 

Electrodes  and  diaphragms  are  kept  in  position  by  a  wooden 
frame-work. 

The  purity  of  the  generated  hydrogen  is  98 '9  per  cent, 
and  that  of  the  oxygen  97  per  cent.  On  an  average  the 
consumption  of  energy  is  417  K.W.H.  per  cubic  metre  of 
mixed  gases,  and  a  current  output  of  96  per  cent,  is  attained 
with  an  energy  efficiency  of  57  per  cent. 

The  energy  expended  in  generating  3  cubic  metres  of 
the  mixed  gases  in  any  ordinary  plant  is,  on  an  average, 
13-5  K.W.H. 

The  cost  of  a  100  H.P.  Garuti  plant  comprising  50  cells, 
each  using  about  400  amps.,  together  with  two  gasometers, 
is  about  £3000,  and  this  price  is  increased  to  £4000  if  plant 
is  required  for  compressing  the  gases. 

Following  are  particulars  of  a  Garuti  plant  operated  by 
the  Soci6te  1'Oxyhydrique  at  Brussels,  according  to  Wins- 
singer  :  J  Each  amp. -hour  gives  0*4  litre  of  hydrogen  and 
0'2  litre  of  oxygen.  A  plant  taking  350  amps,  at  a 
pressure  of  2*5  volts  gave  3'36  cubic  metres  of  hydrogen 
and  1*68  cubic  metres  of  oxygen  per  24  hours,  requiring  a 
daily  expenditure  of  21,000  watt-hours  or  an  average  of 
4166  watt-hours  per  cubic  metre  of  mixed  gases.  This 
agrees  with  a  current  efficiency  of  96  per  cent,  and  an 
energy  efficiency  of  57  per  cent. 

An  account  of  a  Garuti  plant  used  at  Eome,  by  the  air- 
ship branch  of  the  Italian  army,  for  generating  hydrogen 
is  given  in  the  Jahrbuch  der  EleJctrochemie,  1901,  7,  336. 

In  1902  Garuti  introduced  an  improvement  in  the  dia- 

J  Chem.  Zeit.,  1898,  22,  609. 


ELECTEOLYTIC   HYDROGEN   AND   OXYGEN.      OZONE       13 

phragm  of  the  cell  by  enlarging  the  zone  of  perforations. 
This  facilitated  the  conduction  of  the  current,  and  the 
passage  of  the  liberated  gases  through  the  enlarged  zone 
was  prevented  by  covering  each  side  with  fine-mesh 
metallic  netting. 

In  1903  an  important  addition  was  made  in  the  form  of 
a  special  arrangement  for  purifying  the  evolved  gases  by 
passing  them  over  heated  platinum ;  this  also  included 
testing  lamps  for  continuous  observation  of  the  purity  of 
the  gases. 

THE    SCHTJCKERT  PROCESS.1 

The  process  was  introduced  in  1896.  Iron  tanks  con- 
tain the  electrolyte,  which  is  15  per  cent,  caustic  soda 
solution,  and  the  working  temperature  is  70°  C.  Sheet 
iron  bells  are  employed  to  isolate  the  electrodes  and  collect 
the  gas  evolved. 

Each  tank  takes  about  600  amps,  and  has  the  dimen- 
sions 26"  x  18"  x  14",  so  that  it  holds  about  50  litres. 
Each  pair  of  unlike  iron  electrodes  is  separated  by  strips 
of  good  insulating  material  extending  from  the  top  down- 
wards about  three-quarters  of  the  total  depth.  Between 
these  separating  plates  and  enclosing  the  electrodes  are  the 
iron  bells  which  collect  the  evolved  gas  and  lead  it  away. 

The  plant  is  manufactured  by  the  Elektrizitats  A.  G. 
vorm.  Schuckert  &  Co.,  Nurnberg,  and  standard  types  are 
supplied  to  take  from  100  to  1000  amps. 

1  D.B.P.  80504;  Electrochem.  Ind.,  1903, 1,  579;  Electrochem.  Zeitsch., 
1908,  230,  248. 


14      THE   MANUFACTURE   OF   CHEMICALS   BY  ELECTROLYSIS 

The  following  prices  are  quoted  for  a  plant  giving  10 
cubic  metres,  of  hydrogen  per  hour  : — 

Electrolyser    ....    £470  Accessories — 

Soda 80  2  gas  holders     .        .        .  £400 

Insulating  materials       .        .         20  Wooden  stages  for  cells    .  40 

Scrubbers,  Dryers,  etc.           .         50  Compressors     .        .        .  570 

2  gas  purifying  stoves  and  packing  150  Water  still        ...  40 

£770  £1050 

HAZABD-FLAMAND  PEOCESS.1 

This  process  has  been  worked  successfully  for  some  years 
by  the  Societe  Anonyme  1'Electrolyse  Frangaise.  Glass 
or  porcelain  diaphragms  are  employed  to  ensure  complete 
separation  of  oxygen  and  hydrogen,  and  the  purity  of  the 
generated  oxygen  is  said  to  be  99  per  cent. 

INTERNATIONAL  OXYGEN  Co.,2  NEW  YOEK. 

This  cell  consists  of  an  iron  tank  acting  as  cathode,  and 
from  the  cover  is  suspended  a  perforated  anode  box  made 
of  low-carbon  steel  to  prevent  the  formation  of  spongy  rust. 
The  anode  and  cathode  are  separated  by  an  asbestos 
sack  suspended  from  the  cover. 

Each  cell  takes  about  390  amps,  at  a  pressure  of  2'61 
volts,  and  the  working  temperature  is  30°  C.  The  purity 
of  the  oxygen  is  said  to  be  98'3  per  cent.,  and  each  cell 
gives  over  3  cubic  feet  per  hour. 

A  cell  somewhat  similar  to  this  in  design  is  the  Halter 3 
cell.  An  iron  tank  forms  the  cathode,  and  in  this  an  in- 
verted funnel  or  box-shaped  anode  of  iron  is  suspended, 

1  Electroch&mist  and  Metallurgist,  1903,  3,  837. 

3  Met.  and  Chem.  Eng.,  1911,  9,  471 ;  1916, 14,  108. 

3  U.S.  Pats.  1172885,  1172887  (1916). 


ELECTROLYTIC   HYDROGEN   AND   OXYGEN.      OZONE       15 

from  the  edge  of  which  an  asbestos  sack  diaphragm  hangs 
to  prevent  mixing  of  the  gases.  Cells  of  the  filter-press 
type  have  been  developed  during  recent  years.  The  Inter- 
national Oxy-Hydric  Company x  of  Chicago  makes  a  cell 
of  this  pattern  in  which  the  electrodes,  corrugated  to  in- 
crease their  surface,  are  constructed  of  special  alloy  heavily 
nickel-plated.  The  electrolyte  employed  is  20  per  cent, 
caustic  potash,  and  asbestos  diaphragms  are  used.  Oxygen 
is  generated,  of  99*5  per  cent,  purity,  at  the  rate  of  4  cubic 
feet  per  K.W.H.  Other  plant  of  this  type  is  made  by 
L'Oxyhydrique  Fran9aise'J  and  by  Messrs.  Eycken,  Leroy 
&  Moritz.3 

The  following  cells  of  various  patterns  for  producing  hy- 
drogen and  oxygen  have  been  patented  during  the  last  few 
years,  but  many  of  them  still  await  industrial  development : — 

Cell  of  Siemens  Bros.  &  Obach,  Eng.  Pat.  11973  (1893). 

A  cell  devised  by  K.  J.  Vareille 4  in  which  the  gases  are 
effectively  separated  by  a  system  of  V-shaped  troughs 
which  completely  divide  cathodes  from  anodes. 

The  cell  of  Fischer,  Leuning  &  Collins  described  in  U.S. 
Pat.  1004249  (1911). 

The  Tommasini  System,  U.S.  Pat.  1035060  (1912). 

The  Burdett  System,  U.S.  Pat.  1086804  (1914). 

ELECTROLYTIC  PRODUCTION  OF  OZONE. 

During  the  electrolysis  of  dilute  sulphuric  acid  a  con- 
siderable amount  of  ozone  is  mixed  with  the  oxygen  evolved 

1  Met.  and  Chem.  Eng.,  1916, 14,  288.  2  Fr.  Pat.  459967  (1912). 

3  Ibid.  397319  (1908),  U.S.  Pat,,  603058.          4  Ibid.  355652  (1905). 


16      THE   MANUFACTURE   OF   CHEMICALS  BY  ELECTROLYSIS 

at  a  platinum  anode  if  a  high  current  density  be  main- 
tained. 

The  amount  of  ozone  may  be  increased  by  employing  a 
water-cooled  anode  so  that  the  temperature  in  its  neigh- 
bourhood is  at  0°  C.  or  lower. 

With  a  current  density  of  80  amps,  per  cm.2  and  a  volt- 
age of  7 '5  volts  the  oxygen  evolved  from  15  per  cent, 
sulphuric  acid  contains  28  grams  of  ozone  per  cubic  metre, 
equivalent  to  a  yield  of  71  grams  per  K.W.H.1 

Alkaline  solutions  yield  considerably  less  ozone,  and  are 
not  suitable  for  the  preparation  of  this  gas.2 

A  method  suitable  for  producing  large  quantities  of  ozone 
has  been  devised  by  Archibald  and  Wartenburg  3  in  which 
alternating  current  is  superimposed  upon  the  direct  current 
used  for  electrolysis.  The  amount  of  ozone  obtained  by 
this  means  is  very  much  greater  than  that  produced  by 
direct  current  alone,  and  the  improvement  is  no  doubt  due 
to  the  depolarising  effect  of  the  A.C.  at  the  anode.  This 
same  beneficial  effect  is  made  use  of  in  Wohlwill's  improved 
process  for  gold  refining,  and  this  advantageous  combination 
of  D.C.  and  A.C.  is  referred  to  later 4  in  connection  with 
other  electro-chemical  processes. 

In  an  experimental  run,  a  maximum  yield  was  obtained 
with  an  A.C.  of  6  amps,  and  a  D.C.  of  '25-1  amp.  The 
sulphuric  acid  employed  had  a  density  of  1  '48,  and  the  most 
suitable  current  density  was  found  to  be  33  amps,  per  dm.2 

1  Zeitsch.  anorg.  Chem.,  1907,  52,  202.  2 Ibid.,  1903,  36,  403. 

3  Zeitsch.  Elektrochem.,  1911, 17,  812.  4  Page  73. 


CHAPTEE  II. 

THE  ELECTROLYTIC  PRODUCTION  OF  PER-SALTS  AND 
HYDROGEN  PEROXIDE. 

PERSULPHATE s  AND  PERSULPHURIC  ACID. 

THE  existence  of  highly  oxidised  salts  of  sulphuric  acid 
was  first  demonstrated  by  H.  Marshall l  when  investigating 
the  result  of  electrolysis  of  solutions  of  potassium  sulphate 
in  well-cooled  sulphuric  acid.  He  succeeded  in  preparing 
potassium  and  ammonium  persulphates,  and  he  ascribed  the 
formula  M2S208  to  these  compounds. 

The  preparation  of  the  persulphates  was  further  studied 
by  K.  Elbs 2  in  1893,  when  he  prepared  a  good  yield  of  the 
ammonium  salt  by  electrolysing  a  saturated  solution  of 
the  sulphate  in  1  part  of  sulphuric  acid  and  8  parts  of 
water,  contained  in  a  porous  cell  which  was  immersed  in  a 
vessel  containing  50  per  cent,  sulphuric  acid.  A  lead 
cylinder  cathode  is  employed,  and  a  spiral  of  platinum  dips 
into  the  anode  ammonium  sulphate  solution.  If  the  entire 
cell  be  cooled  by  immersion  in  ice-water  and  an  anode 
current  density  of  50  amps,  be  employed,  the  persulphate 
gradually  separates  in  a  crystalline  form  in  the  anode  com- 
partment. The  cathodic  sulphuric  acid  must  be  renewed 

1  Trans.  Chem.  Soc.t  1891,  59,  771. 

2  Journ.  prakt.  Chem.,  1893,  48,  185. 

(17)  2 


18      THE   MANUFACTURE   OF  CHEMICALS  BY  ELECTROLYSIS 

occasionally  because  its  acidity  becomes  steadily  neutralised 
by  the  alkali  formed  at  the  cathode  during  electrolysis.  It 
is  also  necessary  to  keep  the  ammonia  content  of  the 
anode  liquor  constant  by  continual  addition  of  ammonium 
hydroxide. 

Later,  in  1895,  Elbs  and  Schonherr l  studied  the  forma- 
tion of  persulphuric  acid  itself.  They  found  that  when 
the  density  of  the  acid  employed  is  less  than  1*20  very 
little  persulphuric  acid  is  obtained  by  electrolysis.  In- 
creasing the  acid  content  above  this  value  leads  to  an  in- 
creased yield  of  persulphuric  acid,  and  the  maximum 
quantity  is  obtained  when  acid  of  density  1* 35-1 '50  is  used. 

The  harmful  influence  of  acid  above  this  strength  is 
probably  due  to  the  following  causes :  Concentrated 
acid  is  a  bad  electrical  conductor,  and  the  heat  developed 
by  the  current  in  passing  through  such  an  electrolyte 
causes  partial  destruction  of  the  persulphuric  acid;  the 
persulphuric  acid  formed  at  the  anode  is  not  free  to  move 
rapidly  from  the  anode  and  is  partially  decomposed  there. 
Elbs  emphasised  the  importance  of  maintaining  a  low 
temperature  to  avoid  decomposition.  Marshall2  showed 
in  1897  the  necessity  for  employing  a  high  current  density 
at  the  anode  and  keeping  the  solution  cold.  Presumably, 
the  high  current  density  increases  the  chances  of  two 
(HS04)  or  (KS04)  ions  uniting. 

Miiller  and  Friedberger3  then  prepared  persulphates  in 

1  Zeitsch.  Elektrochem.,  1895,  1,  417,  468. 
2 /.  Soc.  Chem.  Ind.,  1897, 16,  396. 
3  Zeitsch.  Elektrochem.,  1902,  8,  230. 


PEODUCTION   OF  PEE- SALTS  AND  HYDROGEN   PEEOXIDE      19 

an  undivided  cell,  using  chromate  in  the  electrolyte  in 
order  to  retard  the  cathodic  reduction  of  the  persulphate. 
A  current  density  of  50  amps,  per  dm.2  was  employed. 
Only  30  per  cent,  of  potassium  salt  was  obtained,  but  as 
much  as  80  per  cent,  of  ammonium  persulphate  was  formed, 
provided  the  ammonia  liberated  in  the  cathode  compart- 
ment during  the  process  was  neutralised  from  time  to 
time. 

It  was  then  shown  by  M.  G.  Levi 1  that  the  yield  is  not 
diminished  by  allowing  the  temperature  to  rise  as  high  as 
30°  C.,  and  is  almost  independent  of  the  cathode  material 
used,  but  he  found  that  a  new  smooth  platinum  anode 
gives  a  better  yield  than  an  old  one  which  has  a  somewhat 
rough  surface.  A  patent  process  of  1904  claimed  the  use 
of  an  undivided  cell  with  the  addition  of  hydrofluoric  acid, 
under  which  circumstances  E.  Miiller 2  had  shown  that  the 
yield  of  potassium  persulphate  was  equal  to  that  of  the  am- 
monium salt.  This  rendered  possible  the  direct  production 
of  the  potassium  salt  without  relying  on  the  intermediate 
formation  of  ammonium  persulphate  and  subsequent  de- 
composition with  potassium  chloride. 

Platinum  electrodes  are  used,  and  the  increased  yield  is 
related  in  some  way  to  the  increased  anode  potential  caused 
by  the  presence  of  fluoride. 

Further  work  by  E.  Miiller 3  on  the  production  of  per- 
sulphuric  acid  indicated  that  permonosulphuric  acid  or 

1  Zeitsch.  Elektrochem.,  1903,  9,  427. 
*Ibid.  1904,  10,  776;  D.E.P.  155805. 
*Ibid.  1907, 13,  257;  1912, 18,  752. 


20      THE   MANUFACTURE   OF  CHEMICALS  BY  ELECTROLYSIS 

Caro's  acid  (H2S05)  is  formed  by  the  action  of  water  on 
the  persulphuric  acid  first  formed  thus  : — 

H2S208  +  H20  =  H2S05  +  H2S04, 

and  Caro's  acid  is  then  destroyed  by  interaction  with 
hydroxyl  at  the  anode,  and  oxygen  is  evolved : — 
H2S05  +  20H  =  H2S04  +  02  +  H20. 
Current  efficiency  may  be  increased  by  adding  a  substance 
such  as  hydrofluoric  acid  which  raises  the  anode  potential, 
and  also  by  adding  sulphurous  acid  or  hydrogen  sulphide 
which  destroys  Caro's  acid  but  does  not  affect  persulphuric 
acid.  The  addition  of  sulphurous  acid  to  the  point  of 
saturation  in  sulphuric  acid  of  density  1*38  raises  the 
current  efficiency  to  92  per  cent.  The  addition  of  hydro- 
chloric acid  to  the  bath  has  a  beneficial  effect  because  it 
raises  the  anode  potential  and  also  destroys  Caro's  acid, 
and  so  removes  the  harmful  depolarising  effect  of  this 
substance.  It  has  been  shown  that  the  concentration  of 
persulphuric  acid  increases  with  rise  in  current  density,  but 
the  final  concentration  of  Caro's  acid  is  independent  of  the 
current  density. 

According  to  a  patent  claim  of  the  Consortium  fur  Elek- 
trochemie  an  undivided  cell  may  be  used,  and  even  without 
the  addition  of  chromate  or  fluoride  a  high  yield  of  am- 
monium persulphate  may  be  obtained,  provided  the  solu- 
tion is  cooled  and  a  high  current  density  employed  (50 
amps,  per  dm.2).  Under  favourable  conditions  a  40  per 
cent,  solution  of  persulphuric  acid  can  be  obtained  by  direct 
electrolysis  of  sulphuric  acid. 

HYDROGEN  PEROXIDE  is  produced  either  by  decomposing 


PEODUCTION  OF  FEE-SALTS  AND  HYDROGEN   PEROXIDE      21 

electrolytic  persulphuric  acid  by  distillation  under  reduced 
pressure,1  or  an  alkaline  persulphate  solution  is  treated 
with  sulphuric  acid,  and  the  solution  distilled  under  re- 
duced pressure.2  A  solution  containing  10-30  per  cent,  of 
hydrogen  peroxide  can  be  produced  by  this  means. 

A  recent  patent 3  specifies  the  following  conditions : 
Ammonium  hydrogen  sulphate  solution  is  electrolysed  at 
a  temperature  of  7°  C.  with  a  platinum  anode  and  a  lead 
cathode.  If  the  temperature  is  allowed  to  rise  above  15°, 
evolution  of  oxygen  takes  place  and  the  yield  of  persulphate 
is  diminished ;  on  the  other  hand,  a  temperature  below 
7°  C.  causes  increased  resistance  in  the  electrolyte  without 
any  compensating  advantage  as  regards  yield.  The  per- 
sulphate solution  is  then  heated  in  an  autoclave  at 
130-140°  C.  under  a  pressure  of  100  Ib.  per  sq.  inch,  and 
decomposition  ensues  according  to  the  equation  : — 

(NH4)2S208  +  2H20  =  (NH4)2S04  +  H2S04  +  H202. 
The  temperature  is  then  lowered  to  65°  C.,  and  by  sumci- 
ently  lowering  the  pressure  a  solution  of  hydrogen  per- 
oxide distils.     It  is  necessary  to  conduct  the  distillation  in 
an  atmosphere  of  nitrogen. 

Another  process  for  preparing  hydrogen  peroxide 
directly  from  dilute  sulphuric  acid  is  the  subject  of  two 
patents.4  Electrolysis  is  conducted  under  high  pressure 
inside  steel  cylinders,  each  of  which  is  lined  with  a  suitable 
cathode  material,  e.g.  silver  amalgam  or  copper  amalgam. 

1  D.R.P.  199958,  217538,  217539  (1908). 

2  Eng.  Pats.  23158,  23660  (1910).       3  U.S.  Pat.  1195560  (1916). 
4Eng.  Pats.  10476  (1913);  22714  (1914). 


22      THE   MANUFACTURE   OF   CHEMICALS   BY  ELECTEOLYSIS 

The  anode  is  fixed  axially  in  the  cylinder,  and  is  surrounded 
by  a  diaphragm  of  asbestos. 

A  certain  amount  of  oxygen  is  discharged  during  elec- 
trolysis, and  separated  from  the  solution  of  hydrogen  per- 
oxide. 

According  to  another  recent  patent l  a  good  yield  of  am- 
monium persulphate  can  be  obtained  in  a  special  cell  with 
a  platinum  anode  and  a  cathode  of  zinc-aluminium  alloy. 

PERCARBONATE  of  potassium  was  first  prepared  by 
E.  J.  Constam  and  A.  V.  Hansen2  in  1896  by  employing 
a  divided  cell,  similar  to  that  used  for  preparing  ammonium 
persulphate,  fitted  with  platinum  electrodes. 

The  electrolyte  was  a  concentrated  solution  of  potassium 
carbonate  which  occupied  anode  and  cathode  compart- 
ments. At  first  oxygen  was  evolved  plentifully  at  the 
anode,  but  as  the  temperature  was  lowered  this  evolution 
diminished  and  at  -  10°  C.  ceased,  whilst  a  pale  blue 
amorphous  solid  separated  out.  This  solid  proved  to  be 
percarbonate  of  potassium  K2C206,  and  was  apparently 
formed  in  a  similar  manner  to  the  persulphates  by  com- 
bination of  the  anions  KCO'3  discharged  under  the 
influence  of  high  anodic  current  density  at  a  low  tempera- 
ture, 2KC03  =  K2C206. 

It  was  further  shown  by  Hansen 3  that  the  temperature 
may  rise  to  0°  C.  without  diminishing  the  yield,  provided 
the  density  of  the  carbonate  solution,  in  the  neighbourhood 
of  the  anode,  does  not  fall  below  T52.  If  the  current 

1  D.R.P.  276985  (1914).  2  Zeitsch.  Elektrochem.,  1896,  3,  137. 

3  Ibid.,  1897,3,445. 


PRODUCTION   OF  FEE-SALTS   AND  HYDROGEN   PEROXIDE      23 

density  is  1-2  amps,  per  dm.2  the  product  contains  only 
30-50  per  cent  of  percarbonate,  but  with  30-60  amps,  per 
dm.2  the  amount  rises  to  85-95  per  cent.  K2C206.  The 
best  result  is  obtained  by  running  slowly  a  saturated  solu- 
tion of  carbonate  into  the  bottom  of  the  anode  compart- 
ment, and  allowing  the  less  dense  solution  in  which  the 
percarbonate  is  suspended  to  flow  out  at  the  top  of  the 
cell.  A  yield  of  2'2-2*4  grams  per  amp. -hour  is  obtained 
of  87-93  per  cent,  percarbonate.  As  the  solubility  of  am- 
monium and  sodium  carbonates  is  very  small  at  low 
temperatures  it  is  not  possible  to  work  successfully  with 
these  salts,  but  rubidium  carbonate  gives  satisfactory 
results. 

Potassium  percarbonate  should  be  dried  by  draining  on 
porous  earthenware,  and  then  exposing  to  warm  dry  air. 
The  crude  salt  can  be  purified  from  carbonate  by  digestion 
with  potassium  hydroxide  solution  at  about  -  5°  C.,  and  if 
it  be  washed  subsequently  with  alcohol  to  remove  adherent 
potash,  the  purity  reaches  95-99  per  cent. 

SODIUM  PERBORATE  has  been  for  some  time  in  use  mixed 
with  soap,  borax,  alkali,  etc.,  and  is  sold  for  laundry  work 
under  such  names  as  Persil,  Clarax,  and  Ozonite.  It 
possesses  detergent  and  bleaching  properties.  Since  1914 
the  salt  NaB03,  4H20  has  been  produced  by  electrolysis, 
and  many  recent  patents  deal  with  this  process.  Formerly, 
the  only  means  available  for  preparation  was  that  of  mix- 
ing borax  with  hydrogen  peroxide. 

A  suitable  solution  for  preparing  the  salt  is  made  up  of 
45  grams  of  borax  and  120  grams  of  sodium  carbonate  per 


24      THE   MANUFACTURE   OF  CHEMICALS   BY  ELECTROLYSIS 

litre.  With  a  platinum  gauze  anode  and  a  water-cooled 
cathode  at  18°  C.  a  good  yield  of  crystalline  perborate  can  be 
obtained,  and  the  loss  due  to  cathodic  reduction  is  small.1 

If  an  alkali  chromate  and  turkey  red  oil  be  added  to  the 
electrolyte,  the  cathode  reduction  amounts  only  to  that  due 
to  3  per  cent,  of  the  hydrogen  discharged.  A  patent  was 
granted  in  1913  for  producing  alkali  perborate  by  electro- 
lysis, and  others  have  followed. 

The  deleterious  effects  of  iron  salts  can  be  removed,  it  is 
stated,  by  addition  of  stannic  acid  or  sodium  bicarbonate 
to  the  electrolyte.2 

It  is  claimed  that  increased  yields  are  obtained  by  the 
addition  of  alkali  chromate,  calcium  chloride,  and  colloids 
such  as  gelatin  and  gum  arabic ;  further,  a  high  current 
density  at  the  anode  is  desirable.3 

According  to  another  patent 4  a  solution  of  borax  con- 
taining 13-15  per  cent,  of  carbonate  is  electrolysed.  Pre- 
sumably, percarbonate  is  first  formed,  and  this  oxidises 
the  borate  to  perborate.  It  is  necessary  to  saturate  the 
solution  with  borax,  and  solid  perborate  must  also  be 
present.  Metallic  catalysts  which  act  negatively  must  be 
excluded,  but  stannic  acid,  bicarbonate  of  soda  and  mag- 
nesium silicate  act  as  accelerators. 

Another  patent  of  the  same  year 5  follows  similar  lines, 
but  stipulates  that  the  bicarbonate  produced  during 
electrolysis  must  not  be  allowed  to  exceed  70-75  grams 

lZeitsch.  EUUrochem.,  1915,  39,  806. 

a  Eng.  Pat.  14292  (1915).  3  Ibid.  100778  (1916). 

4  Ibid.  100153  (1916).  5  Ibid.  102359  (1916). 


PRODUCTION   OF   FEE-SALTS  AND  HYDEOGEN   PEEOXIDE      25 

per  litre,  or  the  stability  of  the  perborate  will  be  affected. 
Free  alkali  is  added,  therefore,  to  the  lye  used,  before  or 
during  electrolysis,  or  the  free  alkali  may  be  replaced  by 
carbonate  of  soda  and  borax,  or  by  metaborate. 

POTASSIUM  PEEMANGANATE  is  now  manufactured  by 
oxidising  the  manganate  solution  in  the  anode  compart- 
ment of  a  divided  cell.  The  first  patents  were  taken  out 
in  1884.  One  by  Theodor  Kemp1  describes  the  use  of 
a  negative  electrode  in  water  at  which  alkali  is  formed, 
the  manganate  solution  in  the  anode  compartment  being 
converted  into  permanganate.  The  anode  and  cathode 
are  separated  by  a  porous  diaphragm. 

The  other  patent  by  E.  Schering2  describes  the  use  of 
a   cement  diaphragm   to   separate   anode  from  cathode. 
Several  advantages  are  evident  over  the  older  process  in 
which  chlorine  or  carbon  dioxide  is  used  to  decompose  the 
manganate  which  results  from  the  fusion  of  manganese 
dioxide  with  chlorate.     These  can  be  shown  by  compar- 
ing the  equations  representing  the  reactions : — 
2K2Mn04  +  C12  =  2KMn04  +  2KC1, 
3K2Mn04  +  2C02  =  2KMn04  +  Mn02  +  2K2C03. 

In  the  electrolytic  oxidation  the  change  is  as  follows  : — 

2K2Mn04  +  0  +  H20  =  2KMn04  +  2KOH. 
It  will  be  observed  that  the  last  oxidation  is  effected  by 
electrolytic  oxygen  liberated  at  the  anode,  no  manganese 
dioxide  is  formed,  and  the  potash  which  is  produced  may 
be  used  again  in  the  fusion  process  for  preparing  more 
manganate. 

JEng.  Pat,  8218  (1884).  2D.R.P.  28782  (1884). 


26      THE   MANUFACTURE   OF  CHEMICALS  BY  ELECTEOLYSIS 

A  cell  used  by  the  Salzbergwerke,1  Stassfiirt,  is  shown 
in  section  in  Fig.  7.  It  is  of  iron,  and  contains  the  solution 
of  manganate,  which  is  replenished  by  gradual  solution 
of  the  fused  product  contained  in  the  metal  baskets 
B.  The  cathodes  are  immersed  in  cement  boxes  C  which 
serve  as  diaphragms,  and  sheet  iron  anodes  A  dip  into  the 
liquor  between  the  metal  baskets  and  the  cement  cathode 


B 


B 


B 


FIG.  7. 

compartments ;  1  kilogram  of  permanganate  requires  about 
0'7  K.W.H.  and  the  voltage  is  about  2'8  volts. 

The  Griesheim  Elektron  Company2  use  a  closed  dia- 
phragm cell  for  preparing  metallic  permanganates,  which 
is  fitted  with  tubes  for  the  escape  of  electrolytic  gas.  Their 
method  for  preparing  the  calcium  salt  is  as  follows  :  The 
cathode  compartment  contains  caustic  potash  solution,  and 
the  anode  compartment  is  filled  with  saturated  manganate 


.P.  101710  (1898). 


1  Ibid.  145368  (1904). 


PRODUCTION   OF  PER- SALTS   AND  HYDROGEN   PEROXIDE      27 

solution.  During  electrolysis,  lime  is  added  in  the  form 
of  a  cream  to  the  anode  compartment,  and  the  perman- 
ganic acid  produced  combines  to  form  the  calcium  salt. 
Hydrogen  and  oxygen  are  evolved  from  the  cathode  and 
anode  respectively.  After  some  time  the  calcium  and 
potassium  permanganates  may  be  separated  by  fractional 
crystallisation.  It  is  possible  to  use  calcium  chloride 
instead  of  lime,  but  in  that  case  potassium  chloride  is  used 
in  the  cathode  compartment  in  place  of  caustic  potash. 

P.  Askenasy  and  S.  Klonowski1  have  shown  that  the 
diaphragm  may  be  dispensed  with.  In  their  experiments 
a  solution  of  potassium  manganate  containing  80-90 
grams  per  litre  was  electrolysed  at  60°  between  iron  elec- 
trodes ;  the  current  density  at  the  cathode  was  0*8  amp. 
per  cm.2  and  at  the  anode  about  O'l  amp.  Under  these 
conditions  the  cathodic  reducing  action  was  small,  and 
permanganate  crystallised  from  the  solution.  When  the 
calculated  amount  of  current  had  passed,  60  per  cent,  of 
the  manganate  had  been  oxidised,  but  it  was  found  possible 
to  continue  electrolysis  until  75  per  cent,  had  been  changed. 

B.  Lorenz2  has  shown  that  it  is  possible  to  produce 
permanganate  by  electrolysing  a  solution  of  caustic  potash, 
if  a  manganese  or  ferro-manganese  anode  be  used  and 
a  cathode  of  copper  oxide  (the  positive  plate  of  a  cupron 
cell  for  example) . 

The  same  method  can  be  used  for  preparing  potassium 
bichromate  if  the  anode  be  of  ferro- chromium.  In  both 

lZeitsch.  EleJctrochem.,  1910,  16,  170. 
*Zeitsch.  anorg.  Chem.t  1896, 12,  393,  396. 


28      THE   MANUFACTUEE   OF   CHEMICALS  BY  ELECTEOLYSIS 

cases  the  iron  in  the  anode  is  converted  to  ferric  hydroxide 
which  collects  at  the  bottom  of  the  cell. 

POTASSIUM  FEEEICYANIDE  l  can  be  produced  by  the 
electrolytic  oxidation  of  ferrocyanide. 

2K4FeCy6  +  0  +  H20  =  2K3FeCy6  f  2KOH. 
A  saturated  solution  of  ferrocyanide  is  used  at  a  tempera- 
ture of  20°  C.  The  Deutsche  Gold  und  Silber  Scheidean- 
stalt  modify  the  process  by  addition  of  calcium  ferrocyanide 
which  prevents  the  contamination  of  the  end-product 
with  alkali.  H.  von  Hayek2  has  examined  the  process, 
and  shown  that  a  100  per  cent,  yield  may  be  obtained  if 
a  high  current  density  be  used  and  the  anode  rotated, 
whilst  the  electrolyte  is  kept  alkaline  to  prevent  the 
formation  of  free  ferrocyanic  acid. 

The  surface  of  the  anode  should  be  greater  than  that  of 
the  cathode,  and  high  concentration  of  salt  is  necessary  to 
prevent  the  high  current  density  from  producing  secondary 
reactions  and  thus  reducing  the  yield. 

ELECTEOLYTIC  SULPHUEIC  ACID  3  is  produced  and  a  con- 
centration as  high  as  95  per  cent,  obtained  by  oxidising 
sulphurous  acid  in  a  diaphragm  cell  with  a  cylindrical 
nickel  cathode  and  an  anode  of  platinum  gauze.  A  porous 
cup  or  cell  which  acts  as  cathode  is  filled  with  sulphuric 
acid  or  sodium  sulphite,  and  the  outer  anode  compartment 
contains  a  solution  of  sulphur  dioxide  which  is  kept 
saturated  during  the  process  by  passing  in  the  gas  con- 

1  Eng.  Pat.  7426  (1886) ;  Electrical  Beview,  1893,  32,  216. 

*Zeitsch.  anorg.  Chem.,  1901,  39,  240. 

9  M.  de  K.  Thompson,  Met.  and  Chem,  Eng.,  1916,  15,  677. 


PKODUCTION   OF   FEE-SALTS   AND   HYDROGEN   PEROXIDE      29 

tinuously.  The  current  density  used  is  about  1  amp.  per 
dm.2 

SODIUM  SELENATE  can  be  produced  by  electrolytic 
oxidation  of  neutral  selenite  solution.1  On  evaporation 
of  the  solution,  crystals  of  selenate  can  be  obtained  to- 
gether with  a  small  amount  of  selenium.  The  addition  of 
a  small  quantity  of  chromate  to  the  bath  prevents  the 
cathodic  deposition  of  selenium.  F.  Foerster2  had 
previously  shown  that  neutral  sulphites  give,  by  electro- 
lytic oxidation,  both  sulphate  and  dithionate.  No  dithion- 
ate  analogue  was  found  by  Miiller  when  oxidising  the 
selenites,  and  in  attempting  to  oxidise  sodium  tellurite  a 
considerable  amount  of  free  tellurium  was  obtained. 

It  may  be  remarked  that  descriptions  in  patent  specifi- 
cations do  not  necessarily  represent  the  process  as  carried 
out  in  practice,  and  in  some  cases  are  drawn  with  that 
intention.  They  should  therefore  be  accepted  with  caution. 

1  E.  Miiller,  Ber.,  1903,  36,  4262.       2  Ber.,  1902,  35,  2815. 


CHAPTEE  III. 

NITRIC  ACID.    HYDROXYLAMINE.    HYDROSULPHITE 
FLUORINE. 

NITRIC  ACID  can  be  separated  from  the  alkali  nitrate 
present  in  peat  by  a  process  devised  by  M.  A.  Nodon,1  a 
French  engineer.  The  peat  deposits  are  treated  in  situ 
by  electrolysis,  and  the  nitric  acid  which  is  discharged  at 
the  anodes  is  drained  away  to  a  collecting  tank.  Earthen- 
ware pots,  having  a  depth  of  approximately  8  feet  and  a 
diameter  of  16  inches,  are  sunk  in  the  peat  deposit  and 
serve  as  anode  compartments.  Each  pot  is  packed  with 
coke  in  the  centre  of  which  is  embedded  a  central  graphite 
anode,  and  it  also  contains  two  earthenware  tubes,  one  for 
drawing  off  the  nitric  acid  solution  as  formed  d  (Fig.  8), 
and  the  other  e  to  supply  water  in  order  to  make  good 
that  which  is  carried  off  to  the  nitric  acid  tank. 

Corresponding  to  each  anode  cell  are  four  cast  iron 
cathodes  KK,  about  8  feet  long,  which  are  connected 
as  shown  in  Fig.  9.  A  continuous  production  of  acid 
takes  place  during  electrolysis,  and  no  harmful  effect 
is  exerted  upon  the  nitrifying  bacteria,  which  continue 
their  work  of  converting  nitrogenous  matter  into  calcium 
nitrate  without  interruption.  Stakes  of  tarred  wood  g 

1  G.  Dary,  London  Electrical  Review,  1913,  73,  1020 ;  Met.  and  Chem. 

Eng.,  1914, 12,  107. 

(30) 


31 


FIG.  8. 

encase   a   packing  of  limestone  c  which  surrounds  each 
earthenware  anode  cell. 

The  resistance  of  the  peat  electrolyte  is  approximately 


Fia.  9. 


32      THE   MANUFACTURE   OF   CHEMICALS  BY  ELECTROLYSIS 

3  ohms  per  cubic  metre,  and  the  pressure  required  per  cell 
is  10  volts.  The  optimum  temperature  at  which  the 
bacteria  convert  the  maximum  amount  of  nitrogenous 
matter  into  nitrate  is  25°  C.,  and  at  this  temperature  2  per 
cent,  of  the  available  nitrogen  is  converted  into  nitric 
acid.  The  limestone  filling  which  encircles  each  earthen- 
ware pot  serves  to  prevent  the  peat  itself  from  becoming 
acid. 

On  one  deposit,  which  had  an  average  depth  of  6  feet,  a 
yearly  output  of  800  tons  of  nitrate  was  obtained  at  an 
approximate  cost  of  one  penny  per  Ib. 

HYDROXYLAMINE. 

In  1902  it  was  shown  by  J.  Tafel  that  nitric  acid  can 
be  reduced  in  a  divided  cell,  in  the  presence  of  sulphuric 
acid,  in  such  a  manner  as  to  give  a  good  yield  of  hydroxy- 
lamine  sulphate,  and  the  process  was  covered  by  patents 
issued  about  that  time. 

Tafel 1  showed  that  a  mercury  cathode  or  one  of  amal- 
gamated lead  gives  the  best  results.  At  a  platinum 
cathode  very  little  reduction  takes  place,  and  the  products 
are  ammonia  and  hydroxylamine.  According  to  Tafel, 
a  lead  cathode  gives  a  40  per  cent,  conversion  of  nitric 
acid  to  hydroxylamine,  but  with  a  copper  ielectrode  only 
15  per  cent,  reduction  to  this  substance  takes  place,  whilst 
much  ammonia  is  formed. 

Since  hydroxylamine  is  not  reduced  to  ammonia  by  a 
copper  cathode,  it  follows  that  the  reduction  of  nitric  acid 

iZeitsch.  anorg.  Chem.,  1902,  31,  289. 


HYDBOXYLAMINE  3£ 

to  this  gas  is  direct,  and  depends  upon  the  specific  action 
of  the  metal.  For  the  preparation  of  hydroxylamine,  dilute 
nitric  acid  may  be  used,  but  the  strength  of  the  sulphuric 
acid  into  which  the  nitric  acid  is  dropped  or  slowly  run, 
should  not  be  less  than  40  per  cent. 

Tafel  showed  that  the  sulphate  is  comparatively  stable 
in  the  presence  of  sulphuric  acid  even  at  a  temperature  of 
40°  C.  He  obtained  the  hydrochloride  by  using  hydro- 
chloric acid  in  place  of  sulphuric  acid,  and  a  cathode  of 
spongy  tin  gave  satisfactory  results.  The  reduction  may 
be  represented  by  the  equation  : — 

HNOS  +  3Ha  =  NH2OH  +  2H20. 

According  to  the  patents  of  Boehringer  and  Sohne,1  a 
two-compartment  cell  is  employed  containing  50  per  cent, 
sulphuric  acid  in  each  compartment.  The  cathode  is  of 
amalgamated  lead,  whilst  the  anode  is  lead.  A  50  per 
cent,  nitric  acid  solution  is  dropped  into  the  cathode  com- 
partment during  the  passage  of  the  current,  and  the  tem- 
perature kept  below  20°  by  cooling  coils.  The  current 
density  employed  is  60-120  amps,  per  dm.2 

According  to  a  French  patent,2  an  anode  of  platinum 
is  used  with  a  tin  cathode.  Sodium  nitrate  solution  is 
dropped  into  the  cathode  compartment,  and  the  anolyte  is 
sodium  chloride  solution.  The  yield  of  hydroxylamine  is 
said  to  be  60-80  per  cent,  and  chlorine  is  a  by-product. 

A  suitable  arrangement  for  producing  hydrochloride 
on  a  large  scale  is  described  by  E.  H.  Pritchett.3  The 

1  D.B.P.  133457, 137697  (1902).          2Fr.  Pat.  318978,  322943  (1903). 

3  /.  Amer.  Chem.  Soc.,  1916,  38,  2042. 
3 


34      THE   MANUFACTURE   OF   CHEMICALS  BY  ELECTROLYSIS 

cathode  compartment  is  filled  with  three  volumes  of  water 
and  one  volume  of  hydrochloric  acid  (density  =  1 '20).  The 
anode  liquid  is  cooled  by  causing  it  to  circulate  through  a 
lead  pipe  immersed  in  a  freezing  mixture,  which  latter  is 
used  to  cool  the  cathode  liquor. 

The  current  density  used  is  50  amps,  per  dm.2  at  25  volts, 
and  the  nitric  acid  (density  1*4)  mixed  with  one  volume  of 
water  is  run  into  the  cathode  compartment  at  the  rate  of 
30  c.c.  per  hour.  The  reduced  liquor  on  being  evaporated 
in  vacuo  gives  80  per  cent,  of  the  calculated  amount  of 
hydroxylamine  hydrochloride. 

THE  PRODUCTION  OF  NITRITE  FROM  NITRATE. 
The  reduction  of  nitrate  to  nitrite  can  be  accomplished 
satisfactorily,  and  the  process  is  the  subject  of  a  recent 
patent.1  It  has  been  shown  (Miiller  and  Weber) 2  that  in 
a  divided  cell,  smooth  platinum  or  copper  cathodes  reduce 
nitrate  to  nitrite  and  ammonia,  but  platinised  platinum 
gives  much  ammonia  and  little  nitrite.  A  spongy  copper 
or  silver  cathode  was  found  to  give  the  best  results.  With 
a  current  density  of  0'25  amps,  per  dm.2  and  a  concentration 
of  2'3  grams  of  sodium  nitrate  per  litre,  a  current  efficiency 
of  90  per  cent,  was  obtained.  The  current  efficiency  with 
an  amalgamated  copper  cathode  was  found  to  diminish 
when  50  per  cent,  of  the  nitrate  had  been  changed. 
Considerable  care  is  evidently  needed  to  prevent  the  forma- 
tion of  ammonia,  since  it  has  been  shown  by  W.  H.  Easton 3 

1  Eng.  Pat.  16643  (1915) ;  25415  (1913). 

*Zeitsch.  Elektrochem.,  1903,  9,  955,  978  ;  1905,  H,  509, 

3  J.  Amer.  Ch&m.  Soc.,  1903,  25,  1042. 


HYDEOSULPHITE  35 

that  nitrates  may  be  quantitatively  reduced  to  ammonia  by 
electrolysis. 

In  the  patent  referred  to  above,  the  cell  described  is 
suitable  for  the  electrolysis  of  alkali  chloride  and  is  of  the 
bell  type,  but  it  is  particularly  suitable  for  electrolysing 
alkali  nitrate.  Pare  nitric  acid  is  formed  at  the  anode 
inside  the  bell  and  is  removed  by  distillation,  which  is 
effected  by  working  under  reduced  pressure  and  by  heating 
the  bells  with  superheated  steam.  The  nitrite  which  is 
formed  at  the  cathode  is  drawn  off  continuously  and 
separated  outside  the  cell.  The  cell  itself  acts  as  cathode, 
and  the  anode  is  of  such  size  as  to  almost  fill  the  bell  and 
thus  reduce  the  working  space  of  the  electrolyte.  High 
current  density  (16  amps,  per  dm.2),  reduced  pressure  and 
high  temperature,  are  favourable  to  the  distillation  of  a 
large  amount  of  concentrated  nitric  acid. 

SODIUM  HYDEOSULPHITE  (HYPOSULPHITE). 

Many  patents  have  been  granted  for  processes  to  pre- 
pare sodium  hydrosulphite  by  the  electrolytic  reduction 
of  sodium  sulphite. 

The  first  process  was  that  of  P.  Spence  and  Sons  l  in 
1903,  in  which  the  sulphite  was  reduced  by  mixing  it  with 
titanium  trichloride.  The  mixture  was  subsequently 
poured  into  caustic  soda  solution  and  stable  sodium  hydro- 
sulphite  formed,  whilst  the  titanium  was  precipitated  as 
titanic  hydroxide  Ti(OH)4.  This  hydroxide  was  afterwards 
dissolved  in  hydrochloric  acid  and  reduced  by  electrolysis 

1  D.E.P.  141452  (1903). 


36      THE   MANUFACTURE   OF   CHEMICALS   BY  ELECTROLYSIS 

to  the  trichloride  (TiCl3),  which  was  employed  to  reduce  a 
fresh  quantity  of  sulphite. 

Subsequent  investigation  by  Elbs1  and  his  co-workers 
showed  that  it  is  possible  to  prepare  hydrosulphite  by  the 
direct  electrolytic  reduction  of  sulphite,  but  it  was  not 
until  Jellinek,  in  1910,  had  demonstrated  the  importance 
of  current  concentration,2  that  good  yields  were  obtained. 
Jellinek  showed  that  the  decomposition  of  hydrosulphite 
is  not  due  to  cathodic  reduction  but  to  spontaneous  decom- 
position, which  takes  place  according  to  the  following 
equation :  2Na2S204  +  H2O  =  Na2S208  +  2NaHS03,  and 
results  in  the  formation  of  sodium  thiosulphate  and 
bisulphite.  He  succeeded  in  retarding  this  decomposition 
by  increasing  the  current  concentration ;  that  is,  the  ratio 
of  current  employed  to  volume  of  electrolyte. 

Jellinek  also  devised  methods  for  purifying  the  salt  and 
preparing  it  in  a  stable  anhydrous  condition.3  By  saturat- 
ing the  solution  with  common  salt,  hydrated  hydrosulphite 
having  the  composition  Na2S204,  2H20  is  salted  out,  and 
can  be  dehydrated  by  heating  to  60°  C.  under  reduced 
pressure. 

With  a  5N  solution  of  sodium  bisulphite,  Jellinek 
obtained  a  10  per  cent,  solution  of  hydrosulphite,  with  a 
current  efficiency  of  80  per  cent.  The  current  concentra- 
tion he  employed  was  5  amps,  per  100  c.c.  of  cathode 

1  Elbs  and  Becker,  Zeitsch.  Elektrocliem. ,  1904,  10,361;  A.  R.  Frank, 
Zeitsch.  Elektrochem.,  1904, 10,  450. 

2  Ibid.,  1911, 17,  157,  245. 

8  Zeitsch.  anorg.  Chem.,  1911,  70,  93  ;  71,  96. 


FLUOKINE  37 

solution,  and  he  proved  that  current  density  was  of  small 
moment  compared  with  the  importance  of  current  con- 
centration . 

For  large-scale  production  two-compartment  cells  are 
employed,  and  it  is  advisable  to  use  freshly-prepared 
bisulphite  in  the  process. 

According  to  one  patent,1  dilute  sodium  bisulphite  is 
electrolysed  in  the  cathode  compartment,  and  the  addition 
of  neutral  chloride  or  sulphate  is  recommended  in  order  to 
increase  the  yield.  During  electrolysis  the  temperature 
should  be  kept  at  0-5°  C.  and  sulphurous  acid  added  to  the 
electrolyte  continuously. 

According  to  another  patent,2  the  process  may  be  made 
continuous  by  circulating  the  bisulphite  solution  through 
the  cells  from  a  reservoir,  and  when  the  liquor  becomes 
sufficiently  concentrated  the  hydrosulphite  separates  in  a 
solid  form. 

A  French  patent 3  claims  the  utilisation  of  zinc  sponge 
prepared  electrolytically  for  reducing  sulphite  to  hydro- 
sulphite. 

FLUOEINE. 

This  gas  was  isolated  by  H.  Moissan  in  1887,  by  the 
electrolysis  of  anhydrous  hydrofluoric  acid  containing  pot- 
assium fluoride.  This  salt  rendered  the  anhydrous  acid  a 
conductor,  and  the  electrolysis  was  effected  in  apparatus 

1  D.B.P.  276058,  276059  (1912) ;  241991  (1910). 

2  Ibid.  278588  (1912) ;  Eng.  Pat.  13901  (1913). 
8  Fr.  Pat.  467443  (1914). 


38      THE   MANUFACTUBE   OF   CHEMICALS  BY  ELECTEOLYSIS 

constructed  throughout  of  platinum.  Moissan  subse- 
quently showed  that  copper  may  be  employed  instead  of 
platinum,  since  it  becomes  coated  with  copper  fluoride, 

H 


Fig.  10. 

which  protects  the  metal  from  further  corrosion.  Apparatus 
was  designed  by  Moissan  for  producing  fluorine  on  a  large 
scale,  and  a  diagram  of  the  plant,  as  constructed  by  MM. 
Poulenc  Freres  1  of  Paris,  is  shown  in  Fig.  10. 

1  Zeitsch.  Elektrochem.,  1900,  7, 150. 


FLUOEINB  39 

The  hydrofluoric  acid  is  contained  in  a  copper  vessel  B, 
the  inner  surface  of  which  C  acts  as  cathode  and  the  top  of 
which  is  closed  by  a  copper  lid  M,  from  which  it  is  in- 
sulated by  a  rubber  ring  L  and  also  by  rubber  insulation 
round  the  bolts,  b.  The  large  outer  vessel  S  contains  a 
freezing  mixture. 

A  copper  tube  'A,  perforated  round  the  lower  part  by  a 
number  of  small  holes  d,  serves  as  a  diaphragm  to  separate 
the  cathode  from  the  anode  p,  which  is  of  platinum  attached 
to  the  inner  copper  tube  T. 

The  tube  T  communicates  with  the  upper  vessel  N,  which 
also  contains  a  cooling  mixture,  and  the  lower  end  of  this 
anode  vessel  T  is  closed  by  a  copper  plate  g,  which  is 
fastened  on  by  screws  v. 

The  diaphragm  is  in  electrical  connection  with  the  anode 
p  and  at  first,  when  electrolysis  has  commenced,  it  becomes 
coated  with  a  deposit  of  copper  fluoride,  but  then,  being 
insulated  by  this  deposit,  it  acts  as  a  true  diaphragm,  and 
fluorine  is  discharged  only  from  the  anode. 

Copper  tubes  H  and  F  serve  to  carry  away  the  evolved 
hydrogen  and  fluorine. 


CHAPTEK  IV. 

THE  ELECTROLYTIC  PREPARATION  OF  PIGMENTS  AND 
INSOLUBLE  SUBSTANCES. 

THE  production  of  such  substances  as  white  lead,  lead 
sulphate,  oxides,  hydroxides,  and  sulphides  of  the  heavy 
metals,  can  be  effected  by  the  electrolysis  of  a  suitable  solu- 
tion, such  as  sodium  (or  potassium)  nitrate,  chloride,  or 
sulphate,  with  an  attackable  anode  and  a  cathode  of  plati- 
num or  some  metal  not  attacked  by  the  electrolyte. 

For  example,  a  solution  of  sodium  sulphate,  when  electro- 
lysed between  a  copper  anode  and  a  platinum  cathode, 
furnishes  S04  ions  at  the  anode  which  attack  the  copper  and 
produce  copper  sulphate;  simultaneously,  sodium  hydroxide 
is  formed  at  the  cathode  by  the  interaction  of  the  water 
with  the  discharged  sodium.  The  two  substances  react, 
and  copper  hydroxide  is  precipitated. 

The  general  utility  of  this  process  was  outlined  by  R. 
Lorenz l  in  1896.  He  employed  a  bath  of  alkali  chloride, 
nitrate  or  sulphate,  with  a  platinum  cathode  and  an  anode 
of  that  metal,  the  hydroxide  of  which  was  to  be  precipitated. 
This  investigation  established  the  following  facts  :  In  pot- 
assium chloride  solution,  a  copper  anode  gives  yellowish 
cuprous  hydroxide,  whilst  in  a  potassium  nitrate  solution 

1  Zeitsch.  anorg.  Cliem.,  1896, 12,  436. 
(40) 


ELECTROLYTIC   PREPARATION   OF   PIGMENTS  41 

blue  cupric  hydroxide  is  precipitated.  The  following^ 
metallic  anodes  furnish  corresponding  hydroxides :  Silver, 
magnesium,  zinc,  cadmium,  aluminium,  lead,  manganese, 
and  iron.  A  mercury  anode  gives  no  hydroxide  in  pot- 
assium chloride  solution,  but  calomel  (Hg2Cl2)  is  formed  ; 
however,  in  a  potassium  nitrate  solution  a  black  mercury 
compound  is  precipitated.  Thallium  becomes  coated  with 
suboxide,  and  a  brown  precipitate  of  thallium  hydroxide 
is  gradually  formed.  A  tin  anode  in  a  chloride,  sulphate 
or  nitrate  solution,  gives  a  precipitate  of  ortho-stannic  acid. 
Nickel  in  sodium  chloride  solution  gives  green  nickel 
hydroxide,  whilst  antimony  and  bismuth  anodes  are  merely 
coated  with  a  grey  skin. 

One  advantage  of  this  method  of  preparation  of 
hydroxides  is  that  formation  in  a  neutral  solution  renders 
unnecessary  careful  washing  to  free  from  excess  of  alkali, 
which  is  generally  needed  in  ordinary  precipitation  pro- 
cesses. Further,  there  is  no  risk  that  excess  of  alkali  will 
redissolve  the  hydroxide  or  oxide  of  metals  such  as  zinc  or 
aluminium,  and  the  electrolyte  is  re-formed  continuously  so 
that  it  lasts  indefinitely,  and  hence  the  cost  of  alkali  is 
avoided.  The  reaction  in  the  case  of  copper  is  represented 
by  the  equation:  CuCl2  +  2NaOH  =  Cu(OH)2  +  2NaCl. 

Lorenz l  has  shown  that  sulphides  can  be  formed  in  a 
similar  manner  by  employing  a  cathode  of  copper  sulphide 
and  an  anode  of  metal,  the  sulphide  of  which  is  required, 
in  an  aqueous  solution  of  alkali  chloride,  nitrate,  or  sul- 
phate. 

1  Zeitsch.  anorg.  Cheni.,  1896,  12,  442. 


42      THE   MANUFACTUBE   OF   CHEMICALS  BY  ELECTEOLYSIS 

For  example,  a  cadmium  anode  in  sodium  chloride  solu- 
tion yields  cadmium  chloride  by  the  reaction  of  the 
discharged  chlorine  with  the  metal,  whilst  the  hydrogen 
liberated  at  the  cathode  reacts  with  the  copper  sulphide  to 
form  hydrogen  sulphide,  H2  +  Cu2S  =  2Cu  +  H2S,  and 
the  gas  precipitates  cadmium  sulphide. 

In  this  manner  the  sulphides  of  copper,  silver,  cadmium, 
tin,  lead,  iron,  and  nickel  can  be  formed  without  employing 
either  hydrogen  sulphide  or  alkali  sulphide,  and  there  is  no 
necessity  to  wash  the  product  till  free  from  alkali  or  hydro- 
gen sulphide,  because  it  is  formed  in  a  neutral  solution. 

In  those  cases  where  the  anodic  compound  formed  by 
the  action  of  the  discharged  anions  upon  the  anode  metal 
is  insoluble,  i.e.  lead  sulphate  formed  by  the  action  of 
sulphate  ions  upon  a  lead  anode,  the  anode  is  speedily 
covered  with  the  insoluble  product,  and  further  action  is 
prevented.  Luckow1  showed  that  this  difficulty  can  be 
obviated  by  using  a  considerable  quantity  of  a  secondary 
salt  (sodium  chlorate),  the  anions  of  which  attack  the 
anode  and  "  crowd  out  "  the  anions  of  the  primary  salt,  so 
that  precipitation  takes  place  a  short  distance  from  the 
anode,  and  the  product  falls  continuously  to  the  bottom  of 
the  vat  instead  of  clinging  to  the  anode  surface. 

The  use  of  a  secondary  salt  has  been  applied  in  the 
manufacture  of  white  lead.2  Luckow  recommends  as 
electrolyte  a  1*5  per  cent,  solution  of  a  mixture  consist- 

lZeitsch.  Elektrochem.,  1903,  9,  797;  D.B.P.  91707(1897);  105143 
(1899). 

2  Trans.  Amer.  Electrocliem,,  1904,  5,  230;  U.S.  Pat.  644779  (1900). 


ELECTROLYTIC  PREPARATION  OF  PIGMENTS     43 

ing  of  9  parts  of  sodium  chlorate  and  1  part  of  sodium 
carbonate.  Carbon  dioxide  is  passed  in  near  the  cathode 
during  electrolysis,  and  the  anode  of  lead  remains  clean. 
Luckow  employed  a  current  density1  of  0'25  amp.  per  dm.2, 
and  obtained  3' 5-4  kgs.  of  white  lead  per  K.W.H. 

Lead  chromate l  and  lead  sulphate  can  be  produced  in  a 
similar  manner,  but  instead  of  carbon  dioxide  it  is  neces- 
sary to  add  chromic  acid  in  the  first  case,  and  sulphuric 
acid  in  the  second  case,  to  maintain  the  concentration  of 
sodium  chromate  or  sodium  sulphate. 

Cuprous  oxide 2  may  be  formed  by  electrolysing  a  com- 
mon salt  solution  which  contains  a  small  quantity  of  alkali, 
if  a  copper  anode  be  employed.  It  has  been  found  that 
the  formation  of  large  particles  of  dark  colour  is  favoured 
by  low  current  density  and  high  temperature,  whilst  the 
addition  of  a  small  quantity  of  gelatin  diminishes  the  size 
of  the  particles  and  lightens  their  colour.  The  colour  and 
regularity  of  the  product  are  improved  by  the  addition  of 
a  small  quantity  of  sodium  nitrate  to  the  electrolyte.3 
The  nitrate  must  be  replenished  at  intervals  since  it  is 
converted  into  nitrite  during  the  process. 

LEAD  PEROXIDE  4  is  formed  if  between  lead  electrodes 
a  1'5  per  cent,  solution  of  sodium  sulphate  (99*5  parts)  and 
sodium  chlorate  (0'5  part)  be  electrolysed  with  a  current 
density  of  '5  amp.  per  dm.2  Air  should  be  blown  through 
this  solution,  and  it  should  be  acidified  with  sulphuric  acid. 

1  Le  Blanc  and  Bindschedler,  Zeitsch.  Elektrochem.,  1902,  8,  255. 

V.  Phys.  Chem.,  1909, 13,  256,  332. 

3Bng.  Pat.  14310  (1915).  4U.S.  Pat.  626330  (1899). 


44      THE   MANUFACTUEE   OF   CHEMICALS  BY  ELECTEOLYSIS 

WHITE  LEAD  processes  which  have  been  employed  on  an 
industrial  scale  are  as  follows  :  In  the  Gardner l  process, 
worked  at  Millwall,  lead  sheet  anodes  are  packed  between 
graphite  cathodes.  The  lead  and  graphite  are  connected 
by  strips  of  tin  so  that  when  the  acetic  acid  vapours  reach 
the  metal,  electrical  action  takes  place  and  the  conversion 
into  white  lead  is  greatly  accelerated.  The  process  is 
similar  to  the  ordinary  chemical  one,  but  the  time  required 
for  the  formation  of  a  batch  of  white  lead  is  reduced  from 
fourteen  weeks  to  about  five  weeks. 

In  the  process  of  A.  P.  Browne 2  a  10  per  cent,  solution 
of  sodium  nitrate  is  electrolysed  in  a  wooden  cell  which  is 
divided  into  two  compartments.  At  the  lead  anode  N03 
ions  attack  the  metal  forming  lead  nitrate,  and  at  the  copper 
cathode  caustic  soda  is  produced.  These  electrolytically 
prepared  solutions  are  drawn  off  when  a  suitable  concen- 
tration is  reached,  and  by  mixing  them,  hydrated  lead  oxide 
is  precipitated,  which  by  subsequent  treatment  with 
sodium  bicarbonate  is  converted  into  white  lead. 

The  process  of  C.  Woltereck  depends  upon  the  electro- 
lysis of  an  alkaline  solution  of  an  ammonium  salt  of  any 
acid  which  will  form  a  soluble  lead  salt.  For  example, 
ammonium  nitrate  solution  containing  bicarbonate  may  be 
employed  with  a  lead  anode  and  cathode  of  carbon  or  lead. 
Nitrate  of  lead  is  formed  at  the  anode,  and  converted  into 
white  lead  by  the  bicarbonate  present  in  the  electrolyte : — 

3Pb(N03)2  +  6NH4OH  +  2NH4HC03  =  Pb(OH)2,  2PbC03  +  2H20 
+  6NH4NO,  +  2NH4OH. 

1  Electrochemist  and  Metallurgist,  1901,  1,  145. 

2  J.  Amer.  Chem.  Soc.,  1895, 17,  835 ;  U.S.  Pat.  496109,  563555. 


ELECTEOLYTIC  PKEPAKATION  OF  PIGMENTS      45 

C.  F.  Burgess l  and  C.  Hambuechen,  in  1903,  investigated 
the  various  conditions  requisite  for  the  electrolytic  produc- 
tion of  a  good  white  lead.  They  found  that  a  two-compart- 
ment cell  is  necessary  to  obtain  a  pure  product.  When 
lead  anodes  and  sodium  nitrate  solution  are  employed  a 
certain  quantity  of  basic  lead  salt  is  produced,  and  there  is 
not  therefore  a  100  per  cent,  formation  of  pure  lead  nitrate. 
The  reduction  of  sodium  nitrate  at  copper  cathodes  cannot 
be  prevented  so  that  a  certain  amount  of  ammonia  is 
formed,  and  the  solution  being  alkaline  after  a  time, 
plumbates  are  formed  and  a  layer  of  spongy  lead  is  de- 
posited on  the  cathode.  If,  therefore,  the  cathode  com- 
partment be  not  separated  from  the  anode,  the  loosely- 
deposited  cathodic  lead  will  fall  into  the  white  lead  which 
is  collecting  at  the  bottom  of  the  cell. 

It  is  advisable  to  make  the  electrolyte  acid  in  the 
neighbourhood  of  the  anode.  Burgess  and  Hambuechen 
tried  N/10  nitric  acid,  and  found,  after  a  trial  run,  that  the 
cathode  liquor  contained  caustic  soda  25  grams,  ammonia 
3*5  grams,  sodium  nitrite  016  gram,  and  sodium  nitrate 
54'3  grams  per  litre.  The  anode  solution  contained  lead 
nitrate  11 3 '5  grams,  and  sodium  nitrate  57 '6  grams  per 
litre.  According  to  these  authors,  sodium  acetate  gives 
better  results  than  nitrate,  but  of  course  is  more  expensive. 

Isenberg  has  pointed'out  that  in  precipitating  substances 
like  white  lead,  by  anodic  action  and  subsequent  precipita- 
tion in  the  same  vat,  it  is  necessary  to  employ  dilute 

1  Trans.  Amer,  Electrochem.,  1903,  3,  299. 
2Zeitsch.  Elektrochem.,  1903,  9,  275. 


46      THE   MANUFACTUEE   OF  CHEMICALS  BY  ELECTEOLYSIS 

solutions  of  the  precipitating  salt  and  a  low  current 
density,  if  regular  precipitates  are  to  be  obtained  and  the 
formation  of  crusts  avoided. 

But,  on  the  other  hand,  a  more  finely  divided  product  is 
obtained  by  high  concentration  of  the  precipitating  salt 
and  a  high  current  density,  so  that  there  are  two  opposing 
sets  of  conditions  which  must  be  suitably  adjusted  to  ob- 
tain a  good  product. 

ZINC  WHITE  has  been  produced  with  some  success,  and 
a  brief  account  of  the  processes  employed  has  been  given 
by  E.  Leriche.1 

It  is  certainly  difficult  to  prepare  by  electrolysis  a  white 
lead  as  good  as  that  formed  in  the  older  Dutch  process. 
This  aspect  of  the  problem  was  discussed  after  a  paper 
read  by  F.  M.  Perkin 2  before  the  Paint  and  Varnish  Society 
in  1911. 

THE  SEPAEATION  OF  THE  EAEE  EAETH  OXIDES. 
Kecent  work  by  L.  M.  Dennis3  and  his  co-workers  has 
shown  that  electrolysis  may  be  of  considerable  value  in 
effecting  a  complete  or  partial  separation  of  the  oxides  of 
the  rare  earth  metals.  From  a  neutral  solution  of  the 
nitrates  of  neodymium,  praseodymium,  lanthanum,  and 
samarium,  nearly  all  the  lanthanum  is  deposited  as  hy- 
droxide in  the  last  fractions  discharged  on  the  cathode. 
The  hydroxides  are  deposited  fractionally  in  order  of  their 
basicity,  and  the  deposition  is  not  dependent  upon  the 

1  Int.  Cong.  App.  Chem.,  1909,  X,  45. 

2  Oil  and  Colour  Trades  Journal,  1911,  39,  457,  578. 
*J.  Amer.  Ghent.  Soc.,  1915,  37,  131,  1963. 


BLECTEOLTTIC  PEEPAEATION  OF  PIGMENTS      47 

ammonia  which  is  formed  by  cathodic  reduction  of  the 
nitric  acid,  because  the  separation  can  be  effected  in  a 
similar  manner  from  a  solution  of  the  chlorides  of  the  rare 
earths. 

A  mercury  cathode  and  a  platinum  or  carbon  anode 
were  employed,  and  a  voltage  of  8-10  volts.  It  was  further 
shown  that  when  a  diaphragm  is  employed  so  that  no  am- 
monia is  produced  by  reduction  of  nitric  acid  the  earths 
are  still  separated  as  before.  Nitrate  solutions  are  pre- 
ferable because  the  deposition  of  the  hydroxides  takes 
place  with  considerably  greater  velocity  than  when  chloride 
solutions  are  employed. 

PYEOPHOEIC  ALLOYS. 

During  an  investigation  of  the  alloys  deposited  by  elec- 
trolysis from  mixtures  of  metallic  salts,  E.  Kremann l  and 
his  co-workers  have  found  that  solutions  of  ferrous  sulphate 
and  magnesium  chloride  in  glycerol-water  mixtures  con- 
taining about  75  per  cent,  of  glycerol,  deposit,  when 
electrolysed,  a  pyrophoric  mixture.  This  consists  of  iron 
and  magnesium  oxides  together  with  carbon  and  hydrogen. 
One  such  cathode  deposit  had  the  following  composition  : 
iron  34*20,  magnesium  8*45,  carbon  5 '26,  hydrogen  1'98, 
and  oxygen  50  per  cent. 

When  the  ratio  of  ferrous  sulphate  (FeS04)  to  magnesium 
chloride  (MgCl2)  is  0'76,  the  deposit  shows  pyrophoric  pro- 
perties, and  these  become  more  pronounced  as  the  ratio 
increases  to  1'25,  after  which  they  diminish  and  entirely 

1  Monats.,  1914,  35,  1387;  1917,  38,  91. 


48      THE   MANUFACTURE   OF   CHEMICALS  BY  ELECTROLYSIS 

disappear  when  the  ratio  reaches  the  value  1'70.  The 
magnesium  in  the  deposit  apparently  does  not  affect  its 
pyrophoric  nature,  but  the  presence  of  carbon  is  essential. 
Current  density  employed  is  usually  0'6-3'3  amps,  per  dm.2 

These  deposits  may  prove  useful  for  the  same  purposes 
as  those  to  which  the  cerium-iron  alloys  (Misch  Metall) 
have  been  adapted. 

By  substituting  cerous  chloride  for  magnesium  chloride 
in  the  solution  the  pyrophoric  nature  of  the  deposit  is  not 
increased.  Temperature  has  considerable  influence,  be- 
cause in  certain  cases  the  deposit  formed  in  the  cold  is  not 
pyrophoric,  whilst  that  produced  at  60°  C.  exhibits  pro- 
nounced pyrophoric  properties.  Analysis  of  these  alloys 
always  shows  the  presence  of  a  small  quantity  of  mag- 
nesium, generally  between  0'4  and  0*5  per  cent. 

TUNGSTEN  BRONZES. 

Complex  tungstates  (polytungstates)  are  formed  at  the 
anode  during  the  electrolysis  of  normal  alkali  tungstates. 
E.  Engels 1  has  shown  that  tungsten  bronzes  can  be  pre- 
pared by  electrolysing  a  fused  mixture  of  tungstic  acid  and 
alkali  carbonate. 

Mixtures  of  barium  and  sodium  tungstates  in  the  molten 
state  give,  with  a  current  density  of  about  4'5  amps,  per 
dm.2  at  a  pressure  of  1*6  volts,  bronzes  which  correspond 
to  the  following  formulae : — 

2BaW4012,  3Na2W5015  and  BaW4012,  5Na2W309. 
This  may  prove  to  be  a  convenient  method  for  preparing 
various  tungsten  bronzes. 

1  Zeitsch.  anorg.  Chem.,  1903,  37,  125. 


CHAPTEE  V. 

ELECTRO-OSMOTIC  AND  ELECTRO-COLLOIDAL  PROCESSES. 

MANY  substances  can  now  be  produced  in  a  pure  condition 
by  electro-osmotic  methods,  that  is,  by  causing  electrolytic 
separation  to  take  place  by  employing  diaphragms  between 
which  the  substance  to  be  treated  is  placed  while  under 
the  influence  of  the  current  passing  between  electrodes 
situated  outside  the  diaphragmed  compartment. 

Crystalloid  substances  can  be  separated  from  colloids, 
and  colloids  may  be  separated  from  each  other  by  utilising 
suitable  diaphragms. 

The  Gesellschaf  t  fur  Electro-Osmose  have  devised  several 
processes  since  1912,  and  it  is  evident  that  practice  is  in 
advance  of  theory  in  this  sphere  of  work,  for  it  was  not 
until  1914  that  papers  appeared  which  devoted  attention 
to  the  theoretical  side  of  the  subject. 

The  method  has  been  adapted  to  the  removal  of  liquids 
from  all  classes  of  substances  1  and  is  related  to  the  electro- 
colloidal  processes  which  have  been  devised  for  desiccating 
peat  and  other  materials.2  In  one  process  peat  is  packed 
between  sheet  anodes  and  perforated  sheet  cathodes  so  that 


.R.P.  233281  (1910);  Eng.  Pats.  11626  (1911),  6995  (1914);  Fr.  Pat. 
439271  (1912). 

2  Eng.  Pats.  12431  (1900),  22301  (1901). 

(49)  4 


50      THE   MANUFACTURE   OF   CHEMICALS  BY  ELECTROLYSIS 

during  electrolysis  the  water  driven  towards  the  cathodes 
will  pass  through  these  and  away  from  the  peat.  The 
negative  plates,  therefore,  function  as  filter-plates. 

A  process  similar  to  this  is  one  in  which  electrodes  are 
fitted  in  the  cells  of  a  filter-press,  and  during  filtration  the 
colloidal  particles  in  the  liquor  are  coagulated  at  the  surface 
of  the  electrodes,  and  so  prevented  from  blocking  the  pores 
of  the  filter-cloths.1 

The  separation  of  the  constituents  of  glue  can  be  effected 
by  placing  the  solution  between  diaphragms  so  that,  during 
electrolysis,  inorganic  constituents  migrate  through  the 
diaphragm  leaving  the  albuminoid  material  behind.2 

Separation  of  colloids  from  each  other  is  effected  by  em- 
ploying diaphragms  which  are  charged  electrically  to  various 
potentials,  so  that  certain  colloidal  particles  pass  through 
whilst  others  are  unable  to  penetrate  the  diaphragm.  For 
example,  with  a  viscose  diaphragm  near  the  anode  and  one 
of  parchment  at  the  cathode,  a  mixture  of  sulphuric  and 
lactic  acids  can  be  separated,  because  only  the  sulphuric 
acid  can  permeate  the  viscose  membrane.  Similarly  sugars 
can  be  separated  from  non-sugars  in  crude  sugar-liquors, 
and  a  solution  of  glue  can  be  separated  into  several 
fractions. 

A  process  for  tanning  skins  by  electro-osmosis  has  been 
devised.3  The  skin  is  placed  between  two  suitable  dia- 
phragms selected,  so  that  active  tanning  materials  cannot 
pass  through  them,  whilst  those  substances  which  are  harm- 


it.  angew.  Chem.,  1915,  28,  308. 
2  Eng.  Pats.  21448  (1914),  11823  (1914).  "  Ibid.  19849  (1914). 


ELECTKO-OSMOTIC  AND  ELECTRO-COLLODIAL   PROCESSES     51 

ful,  penetrate  the  diaphragms  under  the  influence  of  the 
current  and  pass  out  of  the  tanning  liquid. 

Silicic  acid,1  in  a  form  which  is  soluble  and  chemically 
pure,  can  be  obtained  by  employing  a  divided  cell  with 
alkali  silicate  in  the  anode  compartment.  Perforated 
electrodes  are  fitted  against  the  diaphragm  wall,  and  during 
electrolysis  alkali  diffuses  into  the  cathode  compartment 
whilst  silicic  acid  remains  in  the  anode  compartment. 
Hydrated  silica  is  thus  separated  in  a  pure  form  specially 
suitable  for  stabilising  colloids. 

Purified  alumina 2  is  prepared  in  a  similar  way  by  neutral- 
ising crude  alkali  aluminate  with  sulphuric  acid,  and  then 
placing  the  gelatinous  mass  in  a  space  which  is  separated 
from  anode  and  cathode  by  diaphragms.  During  electro- 
lysis the  alkali  is  expelled  from  the  alumina  and  passes  to 
the  cathode. 

In  another  process  for  the  electrolytic  lixiviation  of 
animal,  vegetable,  and  mineral  substances,3  electrically 
active  material  is  extracted  by  causing  the  liquor,  in  which 
the  substance  is  suspended,  to  travel  backwards  and  for- 
wards through  perforated  electrodes.  The  negative  and 
positive  constituents  collect  at  their  respective  electrodes. 

A  short  account  of  the  technical  applications  of  electro- 
capillary  processes  has  been  given  recently  by  W.  C.  McC. 
Lewis,4  in  which  mention  is  made  of  many  of  the  above 
processes. 

The  phenomenon  of  electro-osmosis  has  been  investigated 

1  Fr.  Pat.  471678  (1914).  2  Eng.  Pat.  6727  (1915). 

3 D.B.P.  294667  (1915).  « J.  Soc.  Chem.  Ind.,  1916,  575. 


52      THE   MANUFACTURE   OF   CHEMICALS  BY  ELECTROLYSIS 

by  Byers  and  Walter,1  and  other  valuable  contributions  to 
our  knowledge  of  tbis  subject  bave  been  recently  made, 
which  render  important  aid  in  the  study  of  a  process  of 
which  little  is  known  at  the  present  time,  although  its 
industrial  importance  is  considerable. 

The  term  electro-oamosis  refers  to  the  passage  of  a  liquid 
through  a  membrane  during  electrolysis.  The  flow  of 
liquid  through  this  membrane  which  separates  anode  from 
cathode  depends  upon  current  strength,  the  resistance  of 
the  liquid,  and  the  thickness  and  porosity  of  the  membrane. 

Cohen2  has  shown  that  during  electro-osmosis  both 
liquid  and  diaphragm  become  electrically  charged  with 
charges  of  opposite  sign. 

According  to  Bancroft,3  the  charge  on  the  diaphragm, 
which  controls  the  direction  of  the  osmotic  flow,  depends 
upon  the  relative  adsorption  of  anions  and  cathions,  being 
positive  if  cathions  are  adsorbed  to  a  greater  extent  than 
anions.  The  same  view  is  held  by  T.  E.  Briggs,4  who  has 
recently  contributed  an  important  paper  on  this  subject. 

1  J.  Amer.  Chem.  Soc.,  1914,  36,  2284. 

2  Wiedemann's  Annalen,  1898,  64,  217. 

3  Trans.  Ainer.  Ekctrochem.,  1912,  21,  233. 

4  J.  Physical  CJwm.,  1917,  21, 198. 


CHAPTEE  VI. 

ELECTROLYTIC  REDUCTION  OF  ORGANIC  COMPOUNDS. 

A  LARGE  number  of  patents  published  during  the  last 
thirty  years  indicate  that  considerable  activity  has  been 
displayed  in  the  application  of  electrolytic  methods  to  the 
production  of  organic  substances.  Most  of  the  patents 1 
are  of  German  origin,  but  during  the  past  five  years  much 
attention  has  been  devoted  to  this  branch  of  chemistry  in 
other  countries. 

Most  of  the  processes  relate  to  the  reduction  of  organic 
compounds,  particularly  the  reduction  of  nitro-compounds, 
but  oxidation  methods  have  been  utilised  successfully,  and 
in  many  cases  substitution  products  and  dye-stuffs  have 
been  prepared  by  electrolytic  means. 

The  literature  of  electro-chemistry-indicates  that  a  large 
amount  of  research  has  been  conducted  in  connection 
with  the  preparation  of  organic  substances,  and  an  excel- 
lent summary  of  this  work  will  be  found  in  the  text-book 
by  Lob.2 

Much  of  the  work  has  been  conducted  with  platinum 
electrodes  and  with  relatively  expensive  organic  solvents 
of  high  electrical  resistance.  These  conditions  militate 

1  Met.  and  Chem.  Eng.,  1915, 13,  211. 

2  Electrochemistry  of  Organic  Compounds,  Walther  Lob,  1903. 

(53) 


54      THE   MANUFACTURE   OF   CHEMICALS  BY  ELECTROLYSIS 

against  the  utilisation  of  the  methods  in  industrial 
chemistry,  but  fortunately  it  is  possible  to  dispense  with 
platinum  in  most  cases,  and  an  aqueous  emulsion  of  an 
organic  compound  can  be  reduced  efficiently,  provided  the 
electrolyte  be  thoroughly  stirred  during  the  process.  Such 
aqueous  electrolytes  are  good  conductors,  and  by  excluding 
organic  solvents  the  electrical  energy  costs  can  be  reduced 
to  the  dimensions  of  commercial  requirements. 

THE  KEDUCTION  OF  NITRO-COMPOUNDS. 

When  reduced  by  electrolysis,  nitrobenzene  and  its 
hornologues  yield  the  same  products  as  may  be  obtained 
by  the  various  chemical  methods  of  reduction.  Aniline, 
azobenzene,  azoxybenzene,  hydrazobenzene,  and  ^-amino- 
phenol,  as  well  as  phenylhydroxylamine,  can  thus  be  ob- 
tained from  nitrobenzene,  and  most,  if  not  all,  of  these 
products  could  be  prepared  satisfactorily  on  an  industrial 
scale  by  electrolysis,  by  adjusting  the  manner  of  working 
so  that  economy  of  energy  is  combined  with  maximum 
yields.  Many  of  these  products  demand  a  comparatively 
high  price,  so  that  low  power  cost  is  not  so  important  in 
this  class  of  manufacture  as  high  percentage  yields. 

In  concentrated  sulphuric  acid  solution,  Gattermann  l 
and  his  co-workers  have  shown  that  with  platinum  cathodes 
aminohydroxy-bodies  result.  With  diaphragm  cells  in 
which  the  cathode  compartment  is  separated  from  the 
anode,  they  found  that  all  nitro-compounds  in  which  the 

1  Ber.,  1893,  26,  1844,  2810 ;  1894,  27,  1927. 


ELECTEOLYTIC  EEDUCTION   OF  OEGANIC  COMPOUNDS      55 

para  position    is    unoccupied  give  ^-aminophenols,   the 
yield  amounting  to  about  40  per  cent. 

It  is  necessary  to  dilute  the  sulphuric  acid  slightly 
or  to  keep  the  temperature  low,  otherwise  sulphonation 
occurs  and  a  jp-aminophenol  sulphonic  acid  results.1 
Elbs  2  was  the  first  to  prove  that  a  considerable  quantity 
of  aniline  is  formed  at  the  same  time,  and  that  a  lead 
cathode  increases  the  amount  of  this  substance. 

Gattermann  subsequently  proved  that  phenylhydroxyl- 
amine  is  the  primary  reduction  product,  and  this  was  de- 
monstrated by  causing  it  to  combine  with  benzaldehyde 
(which  was  present  during  reduction)  as  fast  as  formed, 
giving  benzylidene-phenylhydroxylamine : — 
C6H5NHOH  +  C6H5CHO  =  C6H5  -  N  -  CH  -  C6H5  +  H20. 

\/ 

With  a  platinum  cathode  in  hydrochloric  acid  suspension 
nitrobenzene  gives  o-  and  ^-chloraniline,  but  Lob3  has 
shown  that  with  a  lead  cathode  aniline  is  the  only  pro- 
duct. Probably  o-  and  ^-chloraniline  result  from  the 
molecular  re-arrangement  of  the  chloramine,  C6H5  -  N HC1, 
which  is  produced  from  the  phenylhydroxylamine  first 
formed.  Elbs  and  Silberman4  also  found  that,  in  acid 
solution,  lead  cathodes  give  more  aniline  than  platinum 
when  reducing  nitrobenzene. 

This  was  confirmed  by  the  reduction  of  the  nitrotoluenes, 

1  Noyes  and  Clement,  Per.,  1893,  26,  990. 

*Zeitsch.  Elektrochem.,  1896,  2,  472. 

3  Ber.,  1896,  29,  1894  ;  Zeitsch.  EleUrochem.,  1898,  4,  430? 

4 I6w2M  1896,  3,  472. 


56      THE   MANUFACTUEE   OF  CHEMICALS  BY  ELECTROLYSIS 

which  gave  a  90  per  cent,  yield  of  the  corresponding 
amines  (toluidines),  by  employing  lead  cathodes  in  sul- 
phuric acid.1  Cathodes  of  zinc  and  tin  were  found  suit- 
able also  for  producing  amines  from  nitro-compounds,  and 
two  patents  of  Boehringer  and  Sohne 2  describe  the  use  of 
a  tin  cathode,  or  an  unattackable  cathode  (platinum)  with 
the  addition  of  a  tin  salt  to  the  acid  electrolyte. 

Later,  the  same  firm  patented  the  use  of  powdered  cop- 
per, lead,  iron,  chromium,  and  mercury,  or  the  salts  of 
these  metals,  in  place  of  tin,  and  also  the  use  of  a  tin  cath- 
ode for  reducing  azo-compounds  to  amines.3  A  considerable 
number  of  investigations  were  conducted  about  that  time 
upon  the  effect  of  various  cathodes  on  the  reduction  of 
nitro-compounds.  Lob  *  published  results  in  1901  which 
showed  that  platinum  and  nickel  gave  benzidine  under 
similar  conditions,  but  zinc  and  amalgamated  zinc  favoured 
the  formation  of  aniline,  whilst  graphite  gave  very  little 
benzidine.  In  alcohol-sulphuric  acid  solution  mercury 
gave  a  good  yield  of  benzidine  from  azobenzene,  and  in 
alkaline-alcoholic  solution  mercury  and  nickel  gave  good 
yields  of  azobenzene  by  reducing  nitrobenzene,  whilst  in 
aqueous  alkaline  suspensions  of  nitrobenzene  good  yields 
of  azoxybenzene  were  obtained  with  mercury  and  nickel 
cathodes. 

Alkaline  electrolytes  give  azo-,  azoxy-,  and  hydrazo- 
compounds,  but  if  a  copper  cathode  be  used  and  copper 

lZeitsch.  Elektrochem.t  1901,  7,  589. 

2 D.R.P.,  116942  (1899) ;  117007  (1900).          3  Ibid.  121835  (1900). 

*Zeitsch.  Elektrochem.,  1901,  7,  337,  597. 


ELECTROLYTIC  REDUCTION  OF  ORGANIC   COMPOUNDS      57 

powder  added,  amines  result.1  An  alkaline  suspension  of 
the  nitro-compound  may  be  used  provided  the  liquid  is 
well  stirred  during  electrolysis,  and,  usually,  the  cathode 
compartment  is  separated  from  the  anode  by  a  diaphragm 
of  porous  earthenware  or  asbestos.  However,  in  many 
cases  it  is  possible  to  dispense  with  the  diaphragm,  and 
thus  dimmish  the  resistance  of  the  vat. 

Nickel  or  mercury  cathodes  increase  the  amount  of 
azoxy-  or  azo-body  formed,  but  lead,  zinc,  copper,  and 
tin  favour  the  formation  of  azo-  and  hydrazo-compounds.'2 
Addition  of  copper  powder  to  the  electrolyte  increases 
amine  formation. 

A  German  patent 3  covers  these  results  by  describing 
the  use  of  an  alkaline  suspension  of  nitro-compound  which 
is  stirred  vigorously,  and  oxide  of  zinc,  tin,  or  lead  is  added 
to  the  electrolyte. 

The  electrode  potential  exerts  an  important  influence 
upon  the  course  of  the  reduction,  but  there  is  undoubtedly 
a  catalytic  effect  as  well ;  the  latter  is  particularly  evident 
with  cathodes  of  copper  or  platinum.  Lob 4  and  Haber 5 
consider  that  electrode  potential  is  the  determining  factor, 
but  Tafel 6  emphasises  the  importance  of  the  catalytic 
effect  of  the  electrode  material.  Undoubtedly  the  product 

1  D.B.P.  130742  (1901). 

2  Lob,  Zeitsch.  Elektrochem.,  1902,  8,  778. 

3  D.B.P.  121899,  121900  (1899). 

4  Zeitsch.  physical.  Chem.,  1904,  47,  418. 

5  Zeitsch.  Elektrochem.,  1898,  4,  506. 

6  Zeitsch.  anorg.  Chem.,  1902,  21,  289;  Zeitsch,  Elektrochem.,  1906,  12, 
X12, 


58      THE   MANUFACTUEE   OF   CHEMICALS  BY  ELECTEOLYSIS 

obtained  during  reduction  depends  in  many  cases  entirely 
upon  the  electrode  potential  (potential  difference  between 
the  cathode  and  the  solution  in  which  it  is  immersed),  and 
the  experimental  work  of  Lob  and  Haber  confirms  this. 

The  catalytic  effect  of  copper  is  shown  in  the  reduction 
of  nitrobenzene,  which  at  a  copper  cathode  is  reduced  to 
aniline,  but  while  copper  sponge  under  ordinary  chemical 
conditions  will  reduce  phenyl-hydroxylamine  to  aniline  it 
has  no  effect  upon  nitrobenzene,  and  the  inference  is  that 
in  electrolytic  reduction  phenylhydroxylamine  may  be 
first  formed  by  electrolysis,  and  this  substance  is  then  con- 
verted to  aniline  largely  by  the  catalytic  effect  of  the  copper 
cathode. 

Nitric  acid  is  reduced  electrolytically  to  hydroxylamine 
at  a  lead  cathode,  but  at  a  copper  cathode  ammonia  is  the 
product;  and  since  copper  will  not  reduce  nitric  acid 
chemically  to  hydroxylamine  but  will  reduce  this  substance 
itself  to  ammonia,  it  would  appear  that  the  first  stage  is 
electrolytic,  and  in  the  presence  of  a  copper  cathode  the 
hydroxylamine  is  further  reduced  to  ammonia.  There  is 
room  for  further  investigation  regarding  the  matter. 

Some  recent  work  by  E.  Newbery l  has  provided  a  con- 
siderable number  of  trustworthy  overvoltage  determina- 
tions which  should  prove  valuable  in  choosing  the  proper 
electrode  for  any  given  reduction.  By  overvoltage  is 
understood  the  excess  back  electromotive  force  above  that 
of  a  hydrogen  electrode  in  the  same  electrolyte,  and  this 
has  been  measured  by  direct  comparison  with  a  hydrogen 

1  Trans.  Chem.  Soc.,  1916, 109,  1051. 


ELECTROLYTIC  EEDUCTION  OF  ORGANIC  COMPOUNDS   59 

electrode.  Overvoltage  must  be  distinguished  from  elec- 
trode potential  since  the  latter  term  refers  only  to  the 
potential  difference  between  an  electrode  and  the  solution 
with  which  it  is  in  contact. 

The  reduction  of  nitrobenzene  follows  a  well-defined 
course  as  shown  by  Haber.1  Nitrosobenzene  is  first 
formed,  then  phenylhydroxylamine,  and  finally  aniline  ; 
other  products  are  formed  by  subsequent  condensation. 
Nitrosobenzene  and  phenylhydroxylamine  condense  to 
azoxybenzene,  which  becomes  reduced  to  hydrazoben- 
zene : — 

C6H5NO  +  CtfH6NHOH     -*    CCH5 .  N  .  N  .  C^H, 

\  / 
0 

C6H5  .  N  .  N  .  C6H5  +  2H2  -  C6H5 .  NH  .  NH  .  C6H6  +  H20. 

\  / 
0 

Hydrazobenzene   and  nitrosobenzene   condense   to  form 

azobenzene : — 

2C6H5NH .  NHC6H5  +  2C6H5NO  =  3C6H5N :  NC6H5  +  2H20. 

These  results  were  confirmed  by  Haber  and  Schmidt,2 
who  succeeded  in  separating  phenylhydroxylamine  by  re- 
ducing nitrobenzene  in  an  alcoholic  solution  of  ammonia 
containing  ammonium  chloride. 

By  reduction  in  alcoholic-alkaline  solution,  Elbs  and 
Kopp3  obtained  azo-  and  hydrazobenzene.  They  em- 
ployed a  porous  pot  in  which  a  platinum  anode  was  im- 
mersed in  a  saturated  solution  of  sodium  carbonate.  This 

3  Zeitsch.  Elektrochem.,  1898,  4,  506  ;  Zeitsch.  angew.  Chem.,  1900,  433. 

2  Zeitsch.  physikal.  Chem.,  1900,  32,  271,  283. 

3  Zeitsch.  Elektrochem.,  1898,  5, 108. 


60      THE   MANUFACTURE   OF  CHEMICALS   BY  ELECTEOLYSIS 

was  surrounded  by  a  larger  vessel  containing  sodium 
acetate  dissolved  in  70  per  cent,  alcohol,  and  the  nitro- 
compound.  A  nickel  gauze  cathode  surrounded  the  porous 
pot,  and  with  a  current  density  of  10-16  amps,  per  dm.2, 
a  90  per  cent,  yield  of  azobenzene  was  obtained.  Further 
reduction  gave  hydrazobenzene,  but  it  was  found  advisable 
to  lower  the  current  density  for  this  stage  to  2-3  amps, 
per  dm.2 

This  work  was  extended  by  Elbs  and  his  pupils,1  and 
the  processes  were  protected  by  patents.2  Subsequently 
alcohol  was  dispensed  with  and  aqueous  caustic  soda 
employed.3  For  example,  an  emulsion  of  nitrobenzene  in 
10  per  cent,  aqueous  sodium  hydroxide  may  be  reduced 
with  a  cathode  of  lead  or  nickel  in  a  porous  earthenware 
cell,  with  a  current  density  of  10-12  amps,  per  dm.2  An 
anode  of  graphite  or  lead  may  be  employed  in  an  outer 
containing  vessel  filled  with  sodium  hydroxide  solution  or 
sodium  sulphate.  Azo-  or  hydrazobenzene  is  obtained 
according  to  the  quantity  of  electricity  passed  through,  and 
the  azobenzene  emulsion  can  be  transformed  into  benzi- 
dine  by  acidifying  the  cathode  liquor  and  completing  the 
reduction.4 

According  to  another  patent6  the  diaphragm  is  not 
essential,  and  the  alkaline  emulsion  of  nitro-compound  can 

1  Zeitsch.  Elektrochtm.,  1898, 5, 113 ;  1900,  7, 133, 141,  335  ;  1902,  8,  789. 

2  D.R.P.  100233,  100234  (1898). 

*Ibid.  116467,  116942  (1899) ;  121900  (1900) ;  130742  (1901). 

4  Zeitsch.  Elektrochem.,  1900,  7,  320,  333,  597. 

5  D.B.P.  141535  (1903) ;  Eng.  Pat,  15750  (1915). 


ELECTKOLYTIC  EEDUCTION  OF  OEGANIC  COMPOUNDS   61 

be  reduced  in  an  iron  vessel  which  serves  as  cathode. 
The  liquor  is  vigorously  stirred  by  a  small  iron  anode,  and 
since  the  working  temperature  is  105-115°  C.  the  containing 
vessel  is  closed  with  a  lid  into  which  a  reflux  condenser  is 
fitted.  Small  amounts  of  azoxy-  and  hydrazobenzene 
are  found  in  the  resulting  azobenzene. 

Aminophenols  which  were  formerly  obtained  only  by  the 
reduction  of  nitro-compounds  in  concentrated  sulphuric 
acid  can  now  be  prepared  by  reducing  dilute  acid  sus- 
pensions of  nitro-compounds,  provided  the  mixture  be  well 
stirred  and  the  cathode  surfaces  made  up  of  two  or  more 
metals.  This  improved  process,  which  it  is  claimed  gives 
good  yields  of  amino-hydroxy  bodies,  is  due  to  the  Society 
of  Chemical  Industry,  Basle.1  When  an  indifferent  cathode 
is  employed,  the  addition  of  certain  metals  in  the  form  of 
salts  or  finely  powdered  metal  to  the  electrolyte  increases 
the  yield  of  amine  at  the  expense  of  amino-hydroxy  com- 
pound ;  such  are  copper,  iron,  or  lead  if  added  separately. 
If,  however,  two  at  least  of  these  and  other  metals  be 
added,  reduction  to  aminophenol  is  favoured. 

For  example,  a  lead  cathode  reduces  nitrobenzene  mainly 
to  aniline  in  dilute  sulphuric  acid,  so  that  the  proportion 
of  aniline  to  aminophenol  is  3:2,  but  if  some  powdered 
bismuth  be  added  to  the  cathode  chamber,  the  ratio  of 
aminophenol  to  aniline  becomes  5:1.  The  following  com- 
binations or  alloys  have  been  found  suitable  :  copper- 
mercury,  lead-arsenic,  copper-tin-arsenic. 

In  one  particular  case  a  lead  cylindrical  vessel   was 

1  Bng.  Pat.  18081  (1915). 


62      THE   MANUFACTUKE   OF   CHEMICALS  BY  ELECTROLYSIS 

employed  as  anode,  and  in  this  was  a  porous  pot  which 
contained  a  perforated  cylindrical  copper  cathode  and  a 
suitable  stirrer.  Into  the  cathode  chamber  one  or  more 
rods  of  lead  extended.  The  anode  liquid  was  30  per  cent, 
sulphuric  acid  and  the  cathode  mixture  was  composed  of 
25  litres  sulphuric  acid  (15°  B.)  and  6  kgs.  of  nitro-benzene. 
The  working  temperature  was  80-95°  C.  and  a  current 
density  of  3  amps,  per  dm.2  was  employed  at  a  pressure  of 
3'5  volts. 

The  aniline  formed  simultaneously  can  be  removed  by 
adding  lime,  and  steam-distilling  the  mixture.  After 
filtering  calcium  sulphate  from  the  residue,  crystals  of 
aminophenol  can  be  obtained  by  evaporation.  The  average 
yield  is  reported  to  be  50  per  cent,  of  the  nitrobenzene 
used. 

In  conclusion,  the  following  reductions  should  be  noticed : 
Primary  and  secondary  hydrazines  can  be  formed  satis- 
factorily by  reduction  of  nitroamines.1 

Boehringer  and  Sohne  employ  cathodes  of  tin,  or  copper 
coated  with  tin,  for  reducing  nitro-guanidine  to  amino- 
guanidine.2 

The  reduction  of  nitro-derivatives  of  naphthalene,  an- 
thracene, and  phenanthrene  has  been  investigated  by  J. 
Moller.3 

Oximes  can  be  reduced  to  amines 4  in  50   per  cent. 

1  N.  J.  Backer,  Bee.  Trav.  Chim.,  1912,  31,  1,  142 ;  1913,  32,  39. 

2  D.B.P.  167637  (1912). 

3  Zeitsch.  Elektrochem.,  1901,  7,  741,  797;  Elektrocliem.  Zeitsch.,  1904, 
10,  199,  222. 

4  D.B.P.  141346  (1903). 


ELECTEOLYTIC  EEDUCTION  OF  ORGANIC  COMPOUNDS   63 

sulphuric  acid  solution,  at  temperatures  below  20°  C.,  with 
a  cathode  current  density  of  16  amps,  per  dm.2 

Aliphatic  amines  are  obtained  by  reducing  aldehyde- 
ammonia  compounds  in  neutral  or  ammoniacal  solution, 
or  the  aldehyde  mixed  with  ammonia  or  ammonium  salts 
can  be  electrolysed  directly.1 

EEDUCTION  OF  COMPOUNDS  CONTAINING  THE  CARBONYL 

GROUP. 

Ketones  are  converted  by  electrolytic  reduction  into 
secondary  alcohols  or  pinacones.2  A  mercury  cathode 
gives  a  good  yield  of  the  former  class,  but  other  cathodes 
give  a  mixture 3  of  the  two  compounds. 

Tafel4  has  shown  the  value  of  a  mercury  cathode  for 
obtaining  a  good  yield  of  secondary  alcohol  in  a  dilute 
sulphuric  acid  electrolyte  (40  per  cent.). 

Camphor  which  contains  the  carbonyl  group  gives  the 
secondary  alcohol  borneol,  on  reduction. 

Reduction  of  compounds  of  the  uric  acid  group  which 
contain  a  carbonyl  group  results  in  the  conversion  of 

"/CO  into  ")CH2.    Caffeine,5  for  example,  is  reduced  to 

deoxy caffeine  in  50  per  cent,  sulphuric  acid,  and  suc- 
cinimide 6  is  reduced  under  similar  conditions  to  pyrrolidine. 
Whilst  lead  cathodes  are  satisfactory  for  reducing  suc- 
cinimide,  mercury  cathodes  reduce  caffeine  more  efficiently. 

1  D.R.P.  148054  (1904).  2  Merck,  D.E.P.  113719  (1899). 

3  Zeitsch.  Elektrochem.,  1902,  8,  783.  4  Ibid.  288. 

5  Ber.,  1899,32,686. 

6  Zeitsch.  Physikal  Chem.,  1905,  50,  713;  1906,  54,  433. 


64      THE   MANUFACTUEE   OF  CHEMICALS  BY  ELECTROLYSIS 

Acetanilide  and  its  homologues  undergo  intra-molecular 
rearrangement  when  reduced,  and  the  corresponding 
amines  are  formed  : — l 

NH2 
C6H5 .  NHCOCH3  ->  C«H4<; 

CH2 .  CH3 

In  the  reduction  of  pyridine  and  quinoline  compounds, 
hydrogenation  generally  occurs.2 

An  interesting  application  of  electrolytic  reduction  to 
vat-dyeing  is  the  process  of  the  Farbwerke  vorrn.  Meister 
Lucius  and  Briining,  in  which  alkali  sulphite  is  electro- 
lytically  reduced  in  the  presence  of  indigo.  In  an  acid 
solution,  indigo  white  is  precipitated.3 

£>-Rosaniline 4  can  be  obtained  by  the  electrolytic  reduc- 
tion of  ^-nitrodiaminotriphenylmethane. 

When  nitro-group  and  keto-group  are  both  present  in 
the  compound  to  be  reduced,  the  former  is  preferably 
attacked  so  that  azo-,  azoxy-,  or  amino-keto  compounds 5 
result. 

lBer.t  1899,32,68. 

2D.R.P.  104664  (1898) ;  Zeitsch.  Elektrochem.,  1893,  2,  580. 
3  D.B.P.,  139567  (1902).  4  Ibid.  84607  (1894). 

5Elbs  and  Wogrinz,  Zeitsch.  Elektrochem.,  1903,  9,  428. 


CHAPTER  VII. 

OXIDATION  AND  SUBSTITUTION  OF  ORGANIC  COMPOUNDS. 

ALTHOUGH  many  substances  have  been  produced  by 
oxidation  methods  :  anthraquinone,  vanillin,  saccharin ; 
oxidation  is  not  so  easily  graduated  as  the  reduction  pro- 
cesses. The  overvoltage  of  oxygen  is  relatively  high  at  most 
anodes,  and  frequently  the  compound  to  be  oxidised  is 
decomposed  during  treatment  and  carbon  dioxide  formed. 

Generally,  conditions  can  be  devised  for  oxidising 
alcohols  to  aldehydes  and  to  acids,  and  the  substituent 
side  chains  of  aromatic  compounds  can  be  converted  into 
aldehyde  (CHO)  or  carboxyl  (COOH)  groups. 

For  example  o-cresol  yields  salicylic  acid  : — l 

/OH  /OH 

r  TT  /         -&.  r  TT  / 

^6il4\  >  ^O^X 

XCH3  XCOOH 

A  good  yield  of  ^-nitrobenzoic  acid 2  is  obtained  from 
p-nitrotoluene  if  a  lead  peroxide  anode  be  employed  in 
a  mixture  of  sulphuric  and  acetic  acids.  Investigations 
upon  the  oxidation  of  aromatic  side-chains  have  been 
conducted  by  Smith3  and  also  by  Law  and  Perkin.4 

!Eng.  Pat.  103709  (1917).  2D.E.P.  117129  (1900). 

3  J.  Amer.  Chem.  Soc.,  1900,  22,  723. 

4  Trans.  Farad.  Soc.,  1904,  1,  1;  1905, 1,  251. 

(65)  5 


66      THE   MANUFACTURE   OF  CHEMICALS  BY  ELECTEOLYSIS 

Further  examples  of  successful  oxidation  by  electrolysis 
may  be  indicated  by  reference  to  the  following  patents  :— 

Aniline  and  hydroquinone  can  be  oxidised  to  quinone,1 
and  the  addition  of  a  manganese  salt  to  the  electrolyte 
accelerates  the  oxidation. 

Basic  dyes  are  formed  by  the  oxidation  of  homologues 
of  triamino-triphenylmethane.2 

The  oxidation  of  pyrogallol  in  a  sodium  sulphate  electro- 
lyte yields  purpurogallin.3 

Addition  of  cerium  salts  accelerates  the  electrolytic 
oxidation  of  anthracene,  naphthalene,  and  phenanthrene, 
which  yield  the  corresponding  quinones.4  The  hydro- 
carbons may  be  in  solution  or  in  the  form  of  a  finely 
divided  suspension.  Anthracene,  for  example,  is  oxidised 
to  ANTHEAQUINONE  in  20  per  cent,  sulphuric  acid ;  anode 
current  density  is  about  5  amps,  per  dm.2,  and  by  the 
addition  of  2  per  cent,  of  cerium  sulphate  the  current 
efficiency  5  is  stated  to  reach  nearly  100  per  cent. 

The  revival  of  "  spent  "  chromic  acid  is  closely  connected 
with  these  oxidations,  since  it  has  been  the  practice,  for 
some  time,  to  regenerate  the  chromic  acid  after  use  by 
electrolysis 6 : — 

Cr2(S04)3  +  30  +  5H20  =  2H2Cr04  +  3H2S04. 

For  this  oxidation  the  "  spent  liquors,"  consisting  of  sul- 
phates of  potassium  and  chromium  and  also  free  sulphuric 

1  D.B.P.  117129  (1900).  2  Ibid.  100556  (1897). 

3  Trans.  Chem.  Soc.,  1904,  85>  243.  *  D.R.P.  152063  (1904). 

5Ekctrochem.  Ind.,  1904,  2,  249. 
6  D.R.P.  103860  (1899) ;  Zeitsch.  Elektrochem. ,  1900,  6,  290,  308. 


OXIDATION  AND  SUBSTITUTION  OF  OEGANIC  COMPOUNDS      67 

acid,  are  run  into  the  cathode  compartment  of  the  electro- 
lytic cell.  Here  they  serve  as  cathode  electrolyte,  whilst 
the  previous  liquors  are  oxidised  in  the  anode  compartment 
with  a  lead  anode.  At  the  lead  cathode  which  is  separated 
from  the  anode  by  a  porous  diaphragm,  hydrogen  gas  is 
discharged,  and  the  acidity  of  the  liquor  is  diminished 
whilst  that  of  the  anode  liquor  becomes  increased.  The 
amount  of  Cr203  present  is  generally  about  100  grams  per 
litre  and  the  sulphuric  acid  content  about  300  grams  per 
litre.  A  current  density  of  3  amps,  per  dm.2  is  employed 
and  the  temperature  is  maintained  at  45-60*  C. 

Miiller  and  Soller  l  have  shown  that  the  anode  surface, 
which  is  actually  lead  peroxide,  acts  as  a  catalyst  in  ac- 
celerating the  oxidation. 

Naphthalene  by  similar  treatment  gives  at  first  naphtho- 
quinone,  but  further  oxidation  yields  phthalic  acid. 
Phenanthraquinone  similarly  passes  to  diphenic  acid  and 
benzoic  acid. 

Vanadium 2  compounds  may  be  employed  as  catalysts  in 
oxidation  and  reduction  processes.  For  example,  anthra- 
cene is  oxidised  to  anthraquinone  with  a  lead  anode  in 
20  per  cent,  sulphuric  acid  which  contains  3  per  cent,  of 
vanadic  acid.  Aniline  under  similar  conditions  may  be 
oxidised  to  benzoquinone,  and  the  latter  substance  can  be 
efficiently  reduced  to  hydroquinone.  Azobenzene  and 
azoxybenzene  are  stated  to  give  a  good  yield  of  benzidine 

1  Zeitsch.  Elektrochem.,  1905, 11,  863  ;  1913, 19,  344. 

2  D.R.P.  172654  (1906). 


68      THE   MANUFACTUEE    OF   CHEMICALS  BY  ELECTEOLYSIS 

in  20  per  cent,  sulphuric  acid  in  the  presence  of  vanadic 
acid. 

VANILLIN1  can  be  formed  by  electrolytic  oxidation  of 
the  sodium  salt  of  iso-eugenol.  According  to  the  process 
of  F.  von  Heyden  Nchfg.  a  15  per  cent,  alkaline  solution 
of  the  sodium  salt  forms  the  anolyte,  and  the  cathode  com- 
partment is  filled  with  caustic  soda  solution  (10-20  per 
cent.).  The  temperature  is  maintained  at  60°  C.,  and  the 
lead  peroxide  anode  evidently  acts  as  a  catalyst,  since  with 
platinum  the  discharged  oxygen  is  evolved  without  effect- 
ing the  oxidation  :  — 


C6H3—  OCH3  +  30  =  C6H3—  OCH3  +  CH3COOH. 


SACCHAEIN  2  can  be  produced  by  the  electrolytic  oxida- 
tion of  o-toluenesulphonamide. 

ELECTEOLYTIC  OXIDATION  OF  ALCOHOLS. 

Methyl  alcohol  can  be  oxidised  under  certain  conditions 
to  formaldehyde  with  a  yield  of  80  per  cent.  Elbs  and 
Brunner  3  employed  160  grams  of  methyl  alcohol  and  75 
grams  of  sulphuric  acid  per  litre.  A  smooth  platinum 
anode  with  a  current  density  of  3'75  amps,  per  dm.2  gave 
good  results  at  30°  C.,  whilst  anodes  of  platinised  platinum 
or  lead  peroxide  gave  a  low  yield  of  formaldehyde  and 
much  carbon  dioxide. 

Ethyl  alcohol  in  dilute  sulphuric  acid  gives  small  amounts 

iD.B.P.  92007  (1895)  ;  Electrochem.  Review,  1900,  1,  31. 

2  D  R.P.  85491  (1895).  *  Zeitsch.  Elektrochem.,  1900,  6,  604. 


OXIDATION  AND  SUBSTITUTION  OF  OEGANIC  COMPOUNDS      69 

of  acetaldehyde  and  acetic  acid,  whilst  in  alkaline  solution 
aldehyde  resin  is  formed.  If  platinised  platinum  anodes 
are  used,  a  high  yield  of  acetaldehyde  is  obtained,  whilst  at 
bright  platinum,  only  acetic  acid  results. 

Propyl  alcohol 1  shows  a  somewhat  greater  resistance  to 
oxidation.  Propionic  acid  is  the  chief  product,  and  a  good 
yield  is  obtained  at  platinum  or  lead  peroxide  anodes  in 
sulphuric  acid.  Iso-propyl  alcohol  which  is  more  easily 
oxidised  gives  a  70  per  cent,  yield  of  acetone. 

Iso-amyl  alcohol  is  oxidised  to  ^so-valeric  acid,  and  glycol 2 
gives  glycollic  acid,  trioxymethylene,  and  a  sugar-like  sub- 
stance. 

Glycerol 3  gives  both  glyceric  aldehyde  and  trioxymethy- 
lene in  sulphuric  acid  with  carbon  and  platinum  anodes, 
but  in  alkaline  solution  acrolein  and  acrylic  acid  are 
formed. 

Mannitol  on  oxidation  gives  oxalic  acid,  trioxymethy- 
lene, and  a  sugar-like  substance. 

A  process  was  devised  some  years  ago  by  M.  Moest 4  for 
producing  alcohol  from  fatty  acids,  and  by  subsequent 
oxidation  the  corresponding  aldehydes  or  ketones.  For 
example,  an  organic  acid  in  the  presence  of  an  inorganic 
acid  gives,  as  chief  product,  an  alcohol  containing  one 
carbon  atom  less  than  the  organic  acid.  In  the  presence 
of  sodium  chlorate,  Moest  obtained  a  yield  of  34  per  cent, 
methyl  alcohol  from  sodium  acetate,  with  a  current  density 
of  5-20  amps,  per  dm.2,  whilst  with  a  current  density  of 

1  Zeitsch.  Elektrochem.,  1900,  6,  608.  2  Compt.  rend.,  1876,  82,  562. 

*Amer.  Chem.  /.,  1893, 15,  656.  4  D.B.P.  138442  (1903). 


70      THE    MANUFACTUEE   OF   CHEMICALS  BY   ELECTKOLYSIS 

20-30  amps,  he  obtained  40  per  cent,  of  methyl  alcohol. 
Other  fatty  acids  were  found  to  give  similar  results. 

ELECTROLYTIC  SUBSTITUTION  OF  ORQANIC  COMPOUNDS. 

Substitution  by  chlorine,  bromine,  and  iodine  has  received 
much  attention.  The  most  successful  industrial  application 
is  presented  by  IODOFOBM. 

In  the  older  chemical  process  in  which  alcohol  reacts 
with  iodine  in  the  presence  of  sodium  carbonate,  only  about 
30  per  cent,  of  the  iodine  is  converted  into  iodoform  : — 

CH3 .  CH2OH  +  SNagCOg  +  5I2  +  2H20  =  CHI3  +  9NaHC03  +  7NaI. 

By  electrolysing  a  solution  containing  50  parts  of 
sodium  carbonate,  170  parts  of  potassium  iodide,  and  100 
parts  of  96  per  cent,  alcohol,  with  a  smooth  platinum  anode, 
practically  all  the  iodine  is  generally  used  in  producing 
iodoform : — l 

CH3  •  CH2OH  +  3NaI  +  3H20  =  Na2C03  +  CHI3  +  NaOH  +  5H2. 

The  cathode  should  be  of  lead,  and  encased  in  parchment 
to  prevent  cathode  hydrogen  from  destroying  the  product.2 
The  temperature  should  be  60-70°  C.  and  anode  current 
density  1-2  amps,  per  dm.2  with  a  voltage  of  2-2'5  volts. 
The  iodoform  is  produced  at  the  rate  of  500  grams  per 
kilowatt-hour  (1'3  grams  per  amp.-hour)  and  the  current 
efficiency  is  about  90  per  cent. 

The  conditions  necessary  when  employing  acetone  in- 
stead of  alcohol  have  been  given  by  H.  Abbot.3 

1  D.R.P.  29771  (1884) ;  Eng.  Pat.  8748  (1884). 

2  Zeitsch.  EleUrochem.,  1899,  3,  268. 

3  J.  Physical  Chem.t  1903,  84. 


OXIDATION  AND  SUBSTITUTION  OF  ORGANIC  COMPOUNDS      71 

Bromoform  1  is  obtained  in  a  similar  manner  if  alkali 
bromide  be  employed  in  the  presence  of  alcohol  or  acetone. 
Chloroform  is  produced  by  employing  alkali  chloride  with 
acetone.  Schering's 2  patent  in  this  connection  has  been 
worked  through  and  confirmed  by  Teeple.3  Chloral  is 
produced  if  alcohol  is  used  in  the  presence  of  alkali 
chloride.4 

The  production  of  AZO-DYES  by  electrolysing  an  anode 
liquor  containing  amine,  nitrite,  and  phenol  or  naphthol 
was  worked  out  by  Lob.5 

The  nitrous  acid  liberated  at  the  anode  reacts  with  the 
amine  to  form  a  diazonium  compound,  and  this  immediately 
condenses  with  the  phenolic  substance  which  is  present  to 
produce  the  azo-dye.  Cooling  is  desirable  though  not  so 
important  as  in  the  ordinary  chemical  method,  since  the 
diazonium  compound  couples  with  the  phenol  immediately 
it  is  formed ;  but  a  diaphragm  must  be  used  to  separate 
anode  from  cathode.  Orange  II,  Congo  red,  dianisidine 
blue,  and  many  other  colours  have  been  formed  in  this  way. 

Aromatic  compounds  in  the  presence  of  alkali  halides 
or  solutions  of  halogen  acids  are  usually  substituted  when 
subjected  to  electrolysis.  Phenols  are  readily  substituted, 
and  several  antiseptics  have  been  obtained  in  this  manner. 
From  thymol  in  alkali  solution,  and  in  the  presence  of 

1  Amer.  Chem.  Journ.,  1902,  27,  63 ;  Trans.  Amer.  Elelctrochem.,  1905, 
8,  281. 

2  D.R.P.  29771  (1884). 

3  J.  Amer.  Chem.  Soc.,  1904,  26,  536. 

4  Elektrochem.  Zeitsch.,  1894, 1,  70. 

5  Zeitsch,  Elektrochem. t  1904, 10,  237. 


72      THE   MANUFACTURE   OF   CHEMICALS   BY  ELECTROLYSIS 

potassium  iodide,  the  substitution  compound  dithymol- 
diiodide  (aristol)  l  is  formed.  This  method  has  also  been 
employed  for  obtaining  eosin  and  other  halogen  derivatives 
of  the  fluorescein  group.2  Good  yields  of  excellent  quality, 
it  is  claimed,  can  be  obtained. 

CONDENSATION  BY  ELECTROLYSIS. 

Many  years  ago,  Brown  and  Walker3  found  that  by 
electrolysis  of  mono-esters  of  dibasic  acids,  carbon  dioxide 
was  removed,  and  the  residues  condensed  to  form  a  dibasic 
ester  of  higher  molecular  weight. 

For  example,  ethyl  potassium  malonate  reacts  in  the 
following  manner,  giving  diethylsuccinic  ester : — 

/COOK  CH2'COOC2H5 

2CH2<^  =       |  +  2C02  +  2K. 

COOC2Eu,  CH2 '  COOC2H5 

The  method  has  been  expanded  by  Mulliken  and  Weems,4 
and  also  by  von  Miller  and  Hofer.5 

The  principle  has  been  applied  to  the  preparation  of 
aromatic  compounds  from  the  carboxylic  acid  copper  salts.6 
The  disappearance  of  the  blue  colour  of  the  copper  salt 
indicates  the  completion  of  the  reaction.  Ethylene 
diamine  is  produced  from  the  copper  salt  of  glycine : — 

(CH2NH2COO)2Cu  =  C2H4(NH2)2  +  2C02  +  Cu. 

1  D.B.P.  64405  (1891).  *  Ibid.  108838  (1899). 

3  Annalen,  1891,  261, 107  ;  1893,  274,  41. 

4  Amer.  Chem.  Journ.,  1893, 15,  323  ;  1894, 16,  569. 

5  Ber.,  1895,  28,  2427,  3438.  6  D.B.P.  147943  (1904). 


OXIDATION  AND  SUBSTITUTION  OF  ORGANIC  COMPOUNDS      73 

In  a  similar  manner  the  copper  salt  of  ^-amino-benzoic 
acid  gives  benzidine  :  — 


2C6H4  =     NH2  •  C6H4  •  C6H4  •  NH2  +  2C02. 

XCOO 

ELECTROLYSIS  WITH  ALTERNATING  CURRENT. 

Electrolytic  oxidation  may  be  moderated  by  super- 
imposing alternating  current  upon  direct  current.  0. 
Reitlinger  l  has  shown  that  alternating  current  diminishes 
the  overvoltage  at  the  anode  during  electrolysis,  and  it  is 
thus  possible  to  prepare  oxidation  products  which  are  not 
easily  obtained  by  direct  current  only.  Ethyl  and  propyl 
alcohols  give  aldehydes,  whereas  when  oxidised  with  con- 
tinuous current  only,  the  principal  product  is  the  corre- 
sponding acid. 

From  toluene  suspended  in  dilute  sulphuric  acid  (density 
1'22)  it  is  possible  to  obtain  benzaldehyde  and  benzoic 
acid  if  A.C.  be  superimposed  upon  D.C.,  whereas  with 
D.C.  only,  the  toluene  is  completely  oxidised  to  carbon 
dioxide  and  water.  Similarly  ^-benzaldehyde  sulphonic 
acid  is  obtained  from  toluene  sulphonic  acid. 

By  the  same  method  sulphuric  acid  may  be  made  to 
yield  a  considerable  quantity  of  ozone,  whilst  ammonia 
may  be  oxidised  to  nitrous  acid  (40  per  cent,  yield)  without 
the  formation  of  nitric  acid. 

These  investigations  indicate  that  we  have  here  a  valu- 
able means  of  controlling  oxidation  processes. 

1  Zeitsch.  Elektrochem.,  1914,  20,  261. 


APPENDIX. 

ELECTRICAL  UNITS. 

Ampere  =  A  current  carrying  1  coulomb  per  second. 

Coulomb  =  A  quantity  of  electricity  which  will  deposit  0-001118  gram  of 
silver  from  a  specified  solution  of  silver  nitrate. 
Quantity  =  current  x  time 

=  1  x  T. 

Faraday  =  96,500  coulombs. 
Gram-calorie  =  A  unit  of  energy  =  4-189  joules. 
Horse-power  =  A  unit  of  power  =  746  watts. 
Joule  =  A  unit  of  energy  =  1  watt-second 

=  0-239  gram-calorie. 
Joules  =  volts  x  coulombs. 
Kilowatt-hour  (K.W.H.)  =  A  unit  of  energy  =  1000  watt-hours. 

=  Work  done  in  1  hour  when  the  power  in  the 

circuit  is  1  kilowatt. 

Ohm  =  The  unit  of  resistance.    The  resistance  of  a  column  of  mercury 
106-3  cms.  long,  cross-section  1  mm2  and  weight  14-452  grams  at  0°  C. 
Ohm's  Law  5s  stated  thus :  I  =  E/R  where  I  =  current  strength 

E  =  pressure  in  volts,  R  =  resistance  in  ohms. 
Volt  =  A  unit  of  pressure  or  potential. 

=  The  pressure  necessary  to  send  a  current  of  1  ampere  through  a 

resistance  of  1  ohm. 
Watt  =  A  unit  of  power  =  The  rate  at  which  energy  is  expended  when  an 

unvarying  current  of  1  ampere  flows  under  a  pressure  of  1  volt. 
Watts  =  amperes  x  volts. 
1000  Watts  =  1  kilowatt. 


(75) 


INDEX  OF  AUTHOKS   AND  NAMES  OF   FIEMS. 

JBLLINEK,  36. 


ARCHIBALD  &  Wartenburg,  16. 
Askenasy,  27. 

BACKER,  62. 

Bancroft,  52. 

Boehringer  &  Sohne,  33,  56,  62. 

Briggs,  52. 

Browne,  44. 

Brown  &  Walker,  72. 

Brunner,  68. 

Burgess  &  Hambuechen,  44. 

Byers  &  Walter,  52. 

COHEN,  52. 

Consortium  fur  Elektrochemie,  20. 

Constam,  22. 

D' ARSON  VAL,  4. 
Dary,  G.,  30. 
Del  Proposto,  10. 
Dennis,  46. 

EASTON,  34. 

Elbs,  17,  18,  36,  55. 

Engels,  48. 

FARADAY,  2. 

Farbwerke    vonn.    Meister,    Lucius 

und  Bnining,  64. 
Friedberger,  18. 

GARDNER,  43. 

Garuti,  10. 

Gattermann,  54. 

Gesellschaft  f iir  Elektro-Osmose,  49. 

Griesheim  Elektron  Co.,  26. 


HABER,  57,  59. 
Hansen.  22. 
Hayek  von,  28. 
Hazard-Flamand,  14. 

INTERNATIONAL  Oxygen  Co.,  14. 
Isenberg,  45. 


KREMANN,  47. 

LATCHINOFF,  4. 

Law,  65. 

Le  Blanc,  43. 

Leriche,  46. 

Levi,  19. 

Lewis,  51. 

Lob,  53,  55,  57,  71. 

Lorenz,  27,  40. 

Luckow,  42. 

MARSHALL,  17,  18. 

Moest,  69. 

Moissan,  37. 

Holler,  62. 

Miiller,  18, 19,  29,  34,  67. 


NATIONAL  Oxy-hydric  Co.,  15. 

Newbery,  58. 

Nodon,  30. 

Noyes  &  Clement,  55. 

PERKIN,  F.  M.,  46,  65. 
Pompili,  10. 
Poulenc  Freres,  38. 
Pritchett,  33. 


REITLINGER,  73. 
Benard,  5. 


SALZBERQWERKE,  26. 
Sobering,  25. 
Schmidt,  5. 
Schonherr,  18. 
Schoop,  8. 
Schuckert,  13. 
Smith,  65. 

(77) 


78      THE   MANUFACTTJKE   OF   CHEMICALS  BY  ELECTKOLYSIS 


Societe  1'Oxyhydrique,  12. 
Society     of      Chemical     Industry, 
Basle,  61. 

TAFEL,  32,  33,  57,  63. 
Thompson,  28. 


VAREILLE,  15. 


WlNSSINGER,  12. 

Woltereck,  44. 


SUBJECT  INDEX. 


ACETANILIDE,  reduction  of,  64. 
Alcohols,  oxidation  of,  68. 
Aldehydes,  formation  of,  68,  69. 
Alloys,  pyrophoric,  47. 
Alternating  current,  use  of,  16,  73. 
Alumina,  purification  of,  51. 
Arhinophenols,  formation  of ,  54,  61. 
Ammonium  persulphate,  19,  21. 
Aniline,  formation  of,  55,  61. 
Anthracene,  oxidation  of,  66. 
Anthraquinone,  67. 
Aromatic  side  chain,  oxidation  of,  65. 
Azo-compounds,  formation  of,  56,  59, 

60. 

Azo-dyes,  production  of,  71. 
Azoxy-compounds,  production  of,  59. 

BENZIDINE,  formation  of,  56,  60. 
Bromoform,  formation  of,  71. 
Browne     process    for    white    lead, 
44. 

CADMIUM    sulphide,    formation    of, 

42. 

Carbonyl  group,  reduction  of,  63. 
Catalytic  electrodes,  57,  67. 
Chloral,  formation  of,  71. 
Chloranilines,  formation  of,  55. 
Chloroform,  formation  of,  71. 
Chrome  yellow,  precipitation  of,  43. 
Chromic  acid,  regeneration  of,  66. 
Condensation  by  electrolysis,  72. 
Current  concentration,  36. 

DECOMPOSITION  voltage,  2. 
Dehydration  by  electro-osmosis,  50. 
Deoxycaffeine,  formation  of,  63. 
Dibasic  esters,  formation  of,  72. 
Diazotisation  by  electrolysis,  71. 

ELECTRO-CAPILLARY  processes,  51. 
Electrodes  of  alloy,  27,  61. 
Electrode  potential,  57,  59. 
Electro-osmosis,  49,  52. 


FiLTER-press  cells  for  electrolysis  of 

water,  5,  15. 
Fluorine,  production  of,  37.  — 

Formaldehyde,  production  of,  68. 

GARDNER  process  for  white  lead,  43. 
Garuti  cell  for  electrolysis  of  water, 

10. 
Glue,  separation  of  constituents  of, 

50. 

Glycerol,  oxidation  of,  69. 
Glycol,  oxidation  of,  69. 

HYDRAZINES,  formation  of,  62. 
Hydrazo-compounds,    formation   of, 

59,  60. 
Hydrogen,    electrolytic    production 

of,  2. 

Hydrogen  peroxide,  21. 
Hydrosulphite,  formation  of,  35. 
Hydroxylamine,  formation  of,  32. 

INDIGO,  reduction  of,  64. 
lodoform,  production  of,  70. 

LANTHANUM,  separation  of,  46. 
Lead  chromate,  43. 

—  peroxide,  43. 

—  sulphate,  43. 

MANGANESE  salts,  use  of,  in  oxidation, 

66. 

Mannitol,  oxidation  of,  69. 
Methyl  alcohol,  oxidation  of,  68. 
Misch  metall,  preparation  of,  47. 

NAPHTHALENE,  oxidation  of,  67. 
Nitric  acid  from  peat,  production  of, 

30. 

Nitrites,  formation  of,  34. 
Nitrobenzene,  reduction  of,  54. 
Nitro- compounds,  reduction  of,  54. 
Nodon's  process  for  making  'nitric 

acid,  30, 


(79) 


80 


THE   MANUFACTUBE   OF   CHEMICALS  BY  ELECTEOLYSIS 


OVBBVOLTAGE,  58,  65. 

Oxygen,   electrolytic   production  of, 
Ozone,  production  of,  15. 

PEAT,  dehydration  of,  50. 

—  nitric  acid  from,  30. 
Perborates,  formation  of,  23. 
Percarbonates,  formation  of,  22. 
Permanganates,  formation  of,  25. 
Persulphuric  acid,  formation  of,  17. 
Phenanthrene,  oxidation  of,  66. 
Potassium  ferricyanide,  28. 

—  percarbonate,  preparation  of,  22. 

—  permanganate,     preparation     of, 

25. 

—  persulphate,  preparation  of,  19. 
Power    utilised    in    electrolysis    of 

water,  3. 

Pyridine,  reduction  of,  64. 
Pyrophoric  alloys,  deposition  of,  47. 

QUINOLINE,  reduction  of,  64. 
Quinone,  formation  of,  66,  67. 

BABE  earth  oxides,  separation    of, 

46. 
p-Kosaniline,  formation  of,  64. 


SACCHABIN,  formation  of,  68. 
Schmidt  cell  for  electrolysis  of  wate,. , 

5. 
Schoop  cell  for  electrolysis  of  water, 

8. 
Schuckert    cell    for    electrolysis    of 

water,  13. 

Silicic  acid,  purification  of,  51. 
Sodium  hydrosulphite,  production  of, 

35. 

-  perborate,  production  of,  23. 
—  selenate,  formation  of,  29. 
Sugar  liquors,  purification  of,  50. 
Sulphides,  preparation  of,  42. 
Sulphuric  acid,  preparation  of,  28. 

TANNING  of  skins  by  electro-osmosis, 

50. 

Toluidines,  formation  of,  56. 
Triphenylmethane  dyes,  66. 
Tungsten  bronze,  formation  of,  48. 

VANADIUM,  catalytic  use  of,  67. 
Vanillin,  preparation  of,  68. 

WATEB,  electrolysis  of,  2. 
White  lead,  production  of,  43. 

ZINC  white,  production  of,  46. 


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